Material and tube wall thickness for DIY travel trailer box?

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Greetings, I am new here and have searched without success for the question but if I missed a thread please excuse me and clue me in. I am planning building a DIY, bumper pull, travel trailer that is 30' long from hitch point to bumper and targeting 14000# GVWR. I am having the chassis fabricated for me as that is the really serious part that has to be perfect and I am well aware of my limitations. The trailer skin will be aluminum with the bottom third diamond plate. Inside the trailer I intend to back the 1x1 tube frame with 1x1 wood studs to provide a thicker wall and fastening surfaces. The trailer will be insulated with spray foam once the outer skin is on and the foam will be cut off at the edge of 1x1 wood studs. The purpose of the trailer is to be able to use rutted national forrest roads but not "off roading" per-se. It will have independent axleless suspension to facilitate that. I want the trailer box to be able to handle 100mph wind loads broadside with ease. When it comes to the material of the living quarters box I am in a bit of an internal debate. Do I go with 1x1 thin wall steel or do I go with 1x1 aluminum. With either one, what wall thickness would you guys recommend I use? I am wondering if the lightweight benefits of aluminum outweight the reduced strength of the steel. I can tig weld either material. Suggestions?
Reply:I'd look at commercial RV's (pull type and 5th wheel) and see what type of structure they use. I think the aluminum framed are bigger than 1" tubing. I don't know if it's necessary to use both aluminum and wood for the structure. I have a 5th wheel with a wood structure. One of the advantages of wood is that it's a better insulator than aluminum. One of the sales guys where I bought mine said his aluminum frame would show frost on the outside walls where the frame work was. Wood doesn't do this but is a little heavier.
Reply:

Originally Posted by Welder Dave

I'd look at commercial RV's (pull type and 5th wheel) and see what type of structure they use. I think the aluminum framed are bigger than 1" tubing. I don't know if it's necessary to use both aluminum and wood for the structure. I have a 5th wheel with a wood structure. One of the advantages of wood is that it's a better insulator than aluminum. One of the sales guys where I bought mine said his aluminum frame would show frost on the outside walls where the frame work was. Wood doesn't do this but is a little heavier.
Reply:Steel would be my choice and I m n alum guy. Alum will fatigue in the HAZ under cyclical loads unless you heat treat back to temper. Steel will take repeated flexing. 4130 steel will perform even better with er80 weld filler. That is why airframe chassis builders choose 4130 over regular step or alum. Steel is readily repairable as well. I would choose steel tube 14 gauge welded with er70, or 4130 square tube 16 gauge welded with er80 filler.Weld like a "WELDOR", not a wel-"DERR"

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Reply:

Originally Posted by kraythax

...I intend to back the 1x1 tube frame with 1x1 wood studs...Do I go with 1x1 thin wall steel or do I go with 1x1 aluminum...
Reply:

Originally Posted by ezduzit

I'd go with 1" x 2" steel and slab/sheet foam.
Reply:

Originally Posted by kraythax

I dont want to do that because that will compromise the trailer inside heating and cooling.
Reply:

Originally Posted by ezduzit

No, it won't. But it will substantially increase the structural strength.
Reply:What do you rely on in this case, on durability or on keeping warm?
Reply:I haven't seen a single design that fully satisfies both of these requests. You always have to sacrifice something. Only if it wasn't the Australians doing it, haha. I liked how you noticed their ability to make quality items. Wonderful people! I watched them build a new hotel near me. These guys are real professionals who can solve even the most tricky engineering issues. What they create always looks expensive, beautiful, and of high quality.
Reply:I have been thinking about making a camper trailer using aluminum. Not sure how much I care about insulation. Plan to use steel frame, and build aluminum box on top. Just starting to think about it, but I'm not spending any more money on a leaking piece of manufactured crap.