Building a box...comments please

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I got a project, and am looking for comments and best practices to help make it come off good.  I weld pretty decent, on patch panels, and fabrication such as bracketry, etc.I am building a trailer. the frame is all done up.  Axle and frame are from a 3/4 ton military trailer.  Frame has been cut down to 36"Wx54"L.  Pic of the chassis is at the bottom of this post.On top of the frame, I am going to build a metal box with a hinged weatherproof lid, 36Wx54Lx24H.  I am thinking to build a frame up of 1"x2" 12ga rectangular tube, and use 16ga sheet steel (appx 1/16", 2.550lb/sqft) to sheath the box.I have three major crossmembers on the trailer frame, and figure the box will bolt to the frame in 3 points on each crossmember.  Bolt straight thru, with 1/4" rubber washers to separate box and frame slightly to keep from trapping mud/water and subsequent rusting.  Probably use a heavier gauge steel for the floorboard, like 3/16" (7.650lb/sqft).So, basically a 3' x 4.5' x 2' box, framed in 1x2x12ga tube, sheathed in 16ga, with attached fenders, tubed in 1x2x12ga and probably a heaver, maybe 1/8" steel.  Will also have a tailgate that'll drop down.Any tips for getting it square and straight?  And keeping it that way?Any tips/comments on making the top weathertight?  I figure a 2 to 3" overhang on all sides (turn-down).Any comments on size/thickness of the tubing and sheetmetal?
Reply:lots of questions...(nice starting point) let me think about it...engineering is needed...do we have one here?...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Best way to assure squareness is to measure diagonally.
Reply:Sorry that this is off topic "kaiser715" but do you have an M-715? I was just curious to what you have done to your M-715? My father and I had one for a while but we ended up selling it. I have always sworn that I would buy another one. I think they are totally cool! I had a buddy that had one and he rebuilt the whole thing and put a 4bt in it. That is a great motor for that vehicle. Anyway sorry for hijacking!My PicturesLA 4x4 Forum
Reply:Was it Lee?
Reply:Start with your basic cube tube frame, build it to your specs, then consider adding crossmembers on your frame as bolting points to your trailer, with 4.5' long it might look ok with a middle brace up the sides aswell. How wide is your top flange on the trailer? Consider using square tubing that is close to that size, square is usually easier to work with and will give you easy figuring for your bolt hole measurements. For your fold down rear gate, I would build it so it hinges inside the frame flush to the outside using slightly smaller tubing. That way when the gate sits inside the frame you still have room on your frame to mount an angle iron backing wall for your gate to sit against. Line that backing wall with weatherstrip to keep the water out. Built a tight latching system so that it compresses the weatherstripping nicely when closed.Once you have that completed, build your bottom plate and instal it on your frame, then make your bolt holes through your tubing and floor. Clad your box with the sheetmetal of your choice. cut your sheet to fit between your outside tubes and weld them flush. Grind your welds down and it should look like its all one peice Weatherproofing a top lid will be a bit of a challenge. I assume you want it hinged? I think I would try building a lid that fits overtop your frame and everything, but use a strap hinge at the back to ensure that the lid will move up and away as you open the lid to avoid binding. You don't need to overlap the top very much, just enough to make it difficult for water to sneak in. Again weatherstrip the top. As for the fenders, either make them or buy some prefabs and simply weld them onto your completed box. These are usually fun projects, enjoy.
Reply:Yep, I got one.  Pretty successful in taking it apart and not finishing the project, though.  Something about getting married and building a house in the meantime.    Hope to have it done in the next few months.Yep, Baton Rouge, bet it was Lee.  I got to ride around in that thing on a wheeling trip, one of the best I've seen.
Reply:Good one DP, You got Zap to pause to think! Have you any of the trailer build articles from the "turtle expeditions"? I can't remember which mag ran those (Fourwheeler I think) but they did some in-depth trailer build-up articles. Are you going with one flat top. Two doors on a slope? I am having trouble picturing, sorry.
Reply:Purpose of the cargo box and trailer?How much weight, and of what general type (sand bags, bags of cement, a thousand pounds of esoteric audiophile speakers supported by three spikes,  big rocks from a quarry, etc, etc) do you anticipate sticking in that cargo box?Making the top panel weather-tight?  Many ways to do that, depending on your tooling availability and desired end look of the project.  You -could- just weld the top panel on.  After all, this IS a welding forum.   OK, hinged weather-tight lid as in a tool-box/cross-over box lid?  An over lap where the lid hangs down 2-3 inches down the sides of the box will help a LOT, but I think you'll really need some sort of gasket between the top edges of the box/frame and the underside of the lid.  It could be as simple as putting some self-stick weather-stripping strips on top of the box/frame.  If you want weather-tight, you'll also have to overlap and gasket your tailgate to the box/frame.Since 3/4 ton is just 1500 pounds, looking at your pintle hook and those pretty big Goodyear tires on there I think you have a bit of overkill going on.   Look at the sheet metal in the bed of a pick-up truck.  If the load is anywhere sort of spread out, then even 16 gauge will hold up an awful lot of weight when supported by those three cross-members of the trailer.  Put some length-wise beads with a bead-roller (not a welder  ) on the floor sheet metal (just like on a pick-up truck) and that will stiffen up the floor a lot.  It may bend and dimple some, but it will hold the load up.  But if you want to make the floor out of ~100 pounds of 3/16 sheet, go right ahead.
Reply:Crap!  Posted up a long post, and lost it.    Grrrrr.First, thanks for the replies so far.The M101A2 that I cut down is rated at: payload 1500 lbs cross-country and 3000 lbs on highway.  This trailer had a bent frame corner and other problems, so I figured out what I could do with the remnants of it.I am building this to go behind my CJ5 for camping gear, hence the need to be weatherproof (and hopefully mouse- and bear-proof).  Typically would carry coolers, frosty adult beverages, tent, duffel bags, etc, on-road and off.  Maximum load for a trip would be maybe as high as 400 lbs of stuff.Axle has been cut down to match the width of my narrow-track CJ, and it has the same-size tires (33x12.50) and rims (15x10).  Bed width worked out to 36" after setting my track width and allowing clearance to the frame rails for the tires.Hinged lid will be a single flat panel (with reinforcements of course) that will cover the whole trailer bed (36x54"), and be hinged at the front end.  Will use gas struts to assist and support.Good idea on the beading/ribbing.  I think I have a piece of ~14ga that is ribbed all the way across every 6" or so, that might be big enough for this.
Reply:Everything sounds fine (probably overkill but that don't hurt).  I would break a 90 on the top of the sheets you're using for the sides about an 1" or so.  On the lid break it on all 4 sides to fit snug to your box.   A little weather stripping and you should be sealed.  If you don't have the equiptment to break the material with I think it'd be worth it to take it to a shop and have it broke, you'd be happier in the long run I think.  Shouldn't cost much to have 5pieces done.DewayneDixieland WeldingMM350PLincoln 100Some torchesOther misc. tools
Reply:You might consider having all your 16 ga. material custom sheared and formed.  Some steel suppliers offer it as a secondary service.  You could order 36 inch and 54 inch pieces formed with a double bend top and bottom forming a sort of channel on those edges.  Out of any crops from your sheets order hat sections formed as well as simple angles and channels.  A handy channel would be one inch on the inside so that a tube would fit inside and legs 3/4 inch long.  A 1 by 1 by1 channel is more difficult and I would avoid ordering something that eats up time on a press brake.  The hat sections could be used as stiffeners under your floor or on your side walls.  No need to do continuous welds other than at corners to keep water out.   If you do long continuous welds .... Don't... or you will buckle things and warp the box.   You could order your lid with three edges formed over.  I would avoid having the fourth edge formed because that eats up time on the brake.  You can weld on a formed angle or one of your formed channel for extra rigidity.  Doing it this way your sheets are delivered square and already with built in stiffness.  You can still stitch in some one inch mechanical tubing if you feel it needs it on the inside for added strength.  One located on the inside of your vertical corners would prevent burn through when you weld up the outside.  You have to be very detailed with your order.  You save the cost of buying all that tubing but have to pay for the forming.  It works out about the same only you have a professional looking box.Last edited by lotechman; 12-13-2006 at 01:42 AM.
Reply:Well, now you're changing the box requirements from weather-tight to bear and vermin proof as well.That really is a change in the box's design.  To be bear-proof, you WILL need it to be solid and strong and well-locking.  To be rodent/vermin-proof, you will need it to be built tight.  IIRC, a mouse only needs a space about the size of a quarter to be able to get in.  And weather-stripping will not keep a mouse out, they will just chew right through that!Hmmmm, for bear-proof I'd probably go to 1/8 inch plate/sheet.  Sheet metal really won't stop a bear.  I've seen videos of bears peeling open a car door or trunk or bashing in the window glass to get to the food inside said vehicle.Form the top edges of the box with a brake to make a lip.  It will save a lot of welding and make the box look more 'professional'.  If you want to put a top frame underneath the lips to stiffen and strengthen it even more, then go for it.
Reply:Originally Posted by MoonRiseWell, now you're changing the box requirements from weather-tight to bear and vermin proof as well.
Reply:Originally Posted by gimpyrobbWas it Lee?
Reply:I had an all steel grub/camp gear box many moons ago. Things tended to mold in there in the long term. There would be a light sweat thing going on in certain weather. Hmmmmmmmmm, dunno.
Reply:Originally Posted by SandyI had an all steel grub/camp gear box many moons ago. Things tended to mold in there in the long term. There would be a light sweat thing going on in certain weather. Hmmmmmmmmm, dunno.
Reply:Just posting an update and "Thank you" here.  I've got the frame built up out of 1x1 and some 1x2 14ga tube, and got the tailgate and fenders framed up, too.Everything came out better than I thought as far as squareness.  I appreciate all the advice given.I did end up making it 18" sides instead of 24", because once I started to piece the first side together, the proportions just didn't "look" right.  I experimented a bit, and the 18" looked much better, and still allowed ample height inside for coolers, etc.This week I gotta start getting the skin on it, and cap off a few open tube ends that will show.I'll get some fresh pics of the body frame and start something under the projects forum in the next few days.