Truck Camper Frame Construction from Aluminum Sizing

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Greetings, I haven't been here in quite a while but I had a question that I hope I can solicit your input on. I have been considering building a custom truck camper to go on the back of my f-250 Diesel short bed. I would like to have the ability to lift the camper off the truck in the wild so I would want lift jacks on the camper that could lift and level the camper while in camp. I plan to MIG weld the aluminum members of the camper using my 180HD with a spool gun. I have been putting in some serious time practicing on scrap and I am confident in the welds. My friend who is a pro welder said that they are good. So as I design the camper, I am wondering what size tube I should use for the main frame and areas where the support jacks will be bolted on. The idea is to use 1/8" aluminum square tube.I figure I will need thicker tube in the corners for the jack and on the main box frame that supports the camper and smaller tube on the supports for windows and the like. Internally I have debated a number of strategies for insulation and walls. I debated covering with some firing strips to attach items and then attaching inner wall panelling which is knotty pine wood panelling. Then I would spray the outside with expanding foam insulation and cut off the extra and finally I would adhere the aluminum skin in some manner to the aluminum frame members and finally bolt on the jacks and seal them with silicone. What I am wondering is what size I should use for the framing tube. I was thinking 1" x 1/8" by 2" square tube but now I am wondering if that is just massive overkill strength wise.  I have been looking at other trailers and campers recently and they seem to be using 1" x 1" thin walled tubing for the frame which seems a bit fragile to me. I appreciate you all taking the time to reply and offer your suggestions.
Reply:Another potential idea is to use a riveted or bolted  construction technique. I have been considering these because I know there are issues with welded aluminum but I would have to find a source for the aluminum bolts to prevent galvanic reaction and for the various rivet gussets unless I could fabricate them myself. Does anyone know of a good book on rivet joints? One that is available on the iPad (iBooks or Kindle) would be a plus.
Reply:I'd flip your idea for the walls and instal the outer skin then foam myself. A key to making this all work will be the walls. What you are building is often referred to as a stress skin panel and it will act as a shear wall to carry the loads. The foam and alum skin will form a rigid structure very much like plywood. I was also thinking about some of the rigid fiberglass spun panels they often use underneath dryvit and stucco. They are light weight and rigid. This is the same principal as most box trailers. The shear walls form the structural strength and the tube just serves as members that allow the walls to be attached.2" rigid foam and fiberglass and resin would also work very well and be light weight. The same idea that they do to build boats..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Hmm, thanks for the reply. I was thinking of going with aluminum because of the weight of fiberglass and the fact the I have neither the facilities nor equipment to make a good smooth gel coat on fiberglass. Are the panels you are referring to prefab bed in sheets? Any idea where I could get them?Also any opinion on the framing tube size and wall thickness? Also any opinion on welded vs mechanical joints?!Last edited by yorzaxt; 11-20-2012 at 09:59 AM.
Reply:Ditto what D' said.The reason the mfgr's use thin 1x1 for a frame is the "shell" is a unibody or monocoque design.regarding wall thickness, what R value insulation do you need?  Personally, I'd go with the blue foam board over spray foam for money's sake.  And I'd go with 1/8" thick tubing for the sake of workability, even if a little overkill.  Thin wall tubing isn't as easy to work with.What are the issues of welded aluminum joints that concern you?  Post those, then you'll get your answer why or why not for welding.If it's simply "welds crack", then I'd say "while it could be the weldor, it could also be the design.  This is potentially a moving object subject to external forces which requires extra engineering."  But I don't think aluminum welds crack just because of the process vs riveting.Besides, this isn't "Riveting Web" Last edited by dubl_t; 11-20-2012 at 11:05 AM.Lincoln SA 200Esab Caddy 160Thermal Arc 201TSMiller Dialarc HFI don't like making plans for the day because then the word "premeditated" gets thrown around the courtroom....
Reply:Look into how Lance campers are constructed. They use alu tube framing.
Reply:Originally Posted by dubl_tDitto what D' said.The reason the mfgr's use thin 1x1 for a frame is the "shell" is a unibody or monocoque design.regarding wall thickness, what R value insulation do you need?  Personally, I'd go with the blue foam board over spray foam for money's sake.  And I'd go with 1/8" thick tubing for the sake of workability, even if a little overkill.  Thin wall tubing isn't as easy to work with.What are the issues of welded aluminum joints that concern you?  Post those, then you'll get your answer why or why not for welding.If it's simply "welds crack", then I'd say "while it could be the weldor, it could also be the design.  This is potentially a moving object subject to external forces which requires extra engineering."  But I don't think aluminum welds crack just because of the process vs riveting.Besides, this isn't "Riveting Web"
Reply:Check out some of the build threads on here. Great info !http://www.expeditionportal.com/foru...ition-Trailers
Reply:here's the insulation: http://www.homedepot.com/Building-Ma...|b|15034148797Regarding heat treating the weld, I'm not sure that would be necessary.This is how I see it: the mfgr's of campers and canopys, in general, most likely looked for the best method of construction that would give them the best profit margin.  I don't think they heat treated the welds, nor added gussets where there should have been.  Again, this is just a generalization; they built the stuff as best as they could to still make money.With that in mind, I think you could build your frame out of aluminum tubing by welding, but think about the external forces  and add gussets where you feel necessary.  I think a frame that is both welded "for rigidity" and rivited would defeat the intent and purpose while adding unecessary time and expense.You will already have a "composite" structure in that the skin will add support.The frames that I've seen crack have been in canopies, all thin wall tubing, no gussets, and few attaching points between the frame and the skin.  And of course the doors or hatches that were made of extruded aluminum.I'm hardly an expert on welding aluminum let alone engineering, these are just my observations.  Good luck with your build and post pics.Lincoln SA 200Esab Caddy 160Thermal Arc 201TSMiller Dialarc HFI don't like making plans for the day because then the word "premeditated" gets thrown around the courtroom....
Reply:I think my major concerns are that the frame will be under more stress than your average camper. I intend to take it deep in the back country and I will even be doubling up tie downs to make it very secure. I wont be rock crawling with it (because of balance) but when on very rutted roads, it could receive sudden shocks from hitting ditches and holes and that is why I am being careful. And I hope this doesn't sound arrogant but I don't have a lot of respect for the construction techniques in the RV industry. I have owned or used several trailers and campers and to say they are built what I would consider "cheaply" is an understatement of massive proportions. Thin 1/8" board for cabinet shelves, windows that aren't sealed around the frames and other problems too numerous to mention. In fact the monocoque construction they use with vacubonding is probably good for keeping down labor costs and churning out trailers, but structurally its crap. This is probably why the airstreams of 45 years ago are still on the road and your average modern camper is dead inside 10 years.
Reply:"your average modern camper is dead within 10 years"Is that true? Dead of structural/construction problems? I had the impression that Airstreams are around at least partly b/c they are considered stylish, so there's a fad. I know there's a fair bit of steel in there, since I've seen old ones rusting out. I had the impression that (newer) old campers simply get displaced style-wise... and then sell for nothing on the used market.
Reply:Originally Posted by yorzaxtI think my major concerns are that the frame will be under more stress than your average camper. I intend to take it deep in the back country and I will even be doubling up tie downs to make it very secure. I wont be rock crawling with it (because of balance) but when on very rutted roads, it could receive sudden shocks from hitting ditches and holes and that is why I am being careful. And I hope this doesn't sound arrogant but I don't have a lot of respect for the construction techniques in the RV industry. I have owned or used several trailers and campers and to say they are built what I would consider "cheaply" is an understatement of massive proportions. Thin 1/8" board for cabinet shelves, windows that aren't sealed around the frames and other problems too numerous to mention. In fact the monocoque construction they use with vacubonding is probably good for keeping down labor costs and churning out trailers, but structurally its crap. This is probably why the airstreams of 45 years ago are still on the road and your average modern camper is dead inside 10 years.
Reply:Originally Posted by keithwins"your average modern camper is dead within 10 years"Is that true? Dead of structural/construction problems? I had the impression that Airstreams are around at least partly b/c they are considered stylish, so there's a fad. I know there's a fair bit of steel in there, since I've seen old ones rusting out. I had the impression that (newer) old campers simply get displaced style-wise... and then sell for nothing on the used market.
Reply:Originally Posted by dave powelson"..... the frame will be under more stress than your average camper. I intend to take it deep in the back country and I will even be doubling up tie downs to make it very secure. I wont be rock crawling with it (because of balance) but when on very rutted roads, it could receive sudden shocks from hitting ditches and holes and that is why I am being careful. ......The truck bed on a pickup frame--sees all kinds of twisting and bending as the frame wallops around--even more in rock crawling (some of which may be permanent deformation). A camper shell mounted to said twisting, bending bed, will see the same and a little more.One of the areas that allows some flex and 'give' is the shell bottom to truck bed top, sandwiching high density closed cell foam. Double tie downs won't necessarily buy you anything.If this joint has 'wiggle room', to allow for uP/DOwn flexing and torquing--that's less stresson the shell itself.IOW--a light design as seen by the RV factories--which allows for flex without permanent deformation  is the same direction to consider. All of the camper shell repair items I've seen in 24 years have been issues with stupid abuse or the rear door/window--not main frame structure biz.
Reply:Originally Posted by yorzaxtGood information. Can I ask what IOW stands for? Any suggestions for making such a frame? I was thinking of a space frame based design. A design where nothing is under bending stress but rather compression and tension.
Reply:Originally Posted by yorzaxtAirstreams are not the "average modern camper." They are built individually and with old aircraft construction techniques and even a tiny one is 60k+. I was referring to the fiberglass vacubonded MDF things you find on your typical RV lot.
Reply:Originally Posted by keithwinsSorry, I probably didn't make myself clear. I don't know that much about campers: do you really think most of them die of structural failure within 10 years? I have the impression that they just sort of go out of style.Keith
Reply:Yeah, you need to think of aircraft construction techniques. Got to have flex in those wings or else they'd snap off at cruise speed.Lincoln Idealarc 250 (circa 1962)Lincoln Weldpak 155 w/Mig KitLincoln Squarewave TIG 175