Structural aluminum - worth it?

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I need a new camping trailer. I have an old one from the 60s that has a steel chassis and aluminum body, mostly folded and riveted. I'm considering a 2014 upgrade and using the same concept but a lot of welding and I'm scared to commit to the idea of using aluminum up top when I read about how much the HAZ weakens joins. I've never done structural aluminum like this but it's obviously done all the time so it can't be all bad, right? This would be used on Australian outback roads, so I'm thinking it would be subject to a similar environment to tuna towers - repeated short, sharp vibration for long periods at a time. I would be using a Dynasty 200dx and probably always less than 1/6" material for essentially a box structure with tube frame and sheet panels and hinged and sliding parts with stainless hardware (opening and sliding drawers, compartments, slides, etc). Ally stock in the 5xxx and 6xxx range is most common from the supplier I'm looking at but I can look around if I need to.I guess my question is, how much does the HAZ weaken compared to the parent material? And is it an issue - does it require maintenance, does it fail outright sometimes, etc?If I'm 100+ miles from help and 1000+ miles from home (and welder) and the structure fails I'm SOL and I'm sure I'd have very unhappy travelling companions (me too). Some tracks e.g. people experience shock fade, bolts unthreading, etc. I don't thrash equipment by choice but sometimes you've got a 100 mile track and a destination in mind and you deflate your tires, grit your teeth and do the best you can.If building out of ally is marginal I'll look at alternatives, no problem (e.g. composite panels, glued/riveted).
Reply:Why not steel? Got any design drawings or pics?
Reply:Mainly weight and corrosion protection also an issue being I do a lot of beach trips and live near the beach. I could do sheet steel but I have a constant battle with rust just from the environment around the house. Not as happy with a steel top frame, the lighter the better, but structurally I'd be more comfortable with the strength of the result.Composite panels would be great, but cost is a factor unless I made my own. That's achievable too, with EPS and epoxy/fibreglass/Innegra/d-cell/other materials. But impact resistance against stones on at least some panels would be an issue with composites. I could glue light ally sheet on those panels. But I've never made composites, although I'm pretty familiar with the concept.No design as yet, but something vaguely similar to this. A bit bigger but still in the 10-12' x 8' (body) range.
Reply:I would stay with the steel chassis but the alum top should be fine as long as you use 5000 series filler such as 5356 and 6061-T4 which you can bend with minimal cracking and will age up some in the HAZ after a while. Sounds like a fun project. Consider how aviation panels are fabricated and welded for reference.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Structural skin composite panels made from wood strips, resin, plastic or fiberglass cloth. May be too much labor for a really big trailer, or you may have the time. Google search "strip canoe" or "strip kayak". A friend made a 2 person strip canoe with this method. VERY strong and he could pick it up with one hand and almost hold it straight out. A small wind would blow it around if not weighted. All you need are lots of lengths of any light weight wood. They look really nice when done. Another friend used a sim method to build a 28 foot sail boat.
Reply:Alu  will be fine just make sure to gusset properly and doublers were needed I've built a lot of ocean boats one has 20000hrs of run time on it pounding 2-5ft waves and it hasn't cracked yet so yeah Alu will hold for you
Reply:Thanks for all the advice.
Reply:Semi trailers bounce down the road for millions of miles made out of nothing but aluminum. Most box type semi trailers built now only have steel over the axles and front pin, they used to have steel crossmembers bolted to the sides but they've gone to aluminum for that too now.Yeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band saw