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Thread: Material and tube wall thickness for DIY travel trailer box?

  1. #1
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    Material and tube wall thickness for DIY travel trailer box?

    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?

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    Re: Material and tube wall thickness for DIY travel trailer box?

    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.

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    Re: Material and tube wall thickness for DIY travel trailer box?

    Quote Originally Posted by Welder Dave View Post
    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.
    Thanks for the reply. Sure I am aware that wood is a better insulator, I am also trying to get the strength and stiffness of the aluminum as this wont be a typical trailer rated only for highways. The wood backing is to increase the thickness of the walls and provide an internal thermal insulator for the very issue you mentioned. As for looking at commercial RVs, I have owned half a dozen of them and they are all, frankly, crap. Built cheaply and prone to break easily. The Australians are much better at building high quality stuff. Anything out of Elkhart is a train wreck. Airstream is the exception to the rule but they are highway trailers. Even if I liked them, though, they wouldnt be very inclined to give me details of their fabrication.

    Hence coming here to ask what I think should be just a pure engineering question.

  5. #4
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    Re: Material and tube wall thickness for DIY travel trailer box?

    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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    Re: Material and tube wall thickness for DIY travel trailer box?

    Quote Originally Posted by kraythax View Post
    ...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...
    I'd go with 1" x 2" steel and slab/sheet foam.

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    Re: Material and tube wall thickness for DIY travel trailer box?

    Quote Originally Posted by ezduzit View Post
    I'd go with 1" x 2" steel and slab/sheet foam.
    I dont want to do that because that will compromise the trailer inside heating and cooling.

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    Re: Material and tube wall thickness for DIY travel trailer box?

    Quote Originally Posted by kraythax View Post
    I dont want to do that because that will compromise the trailer inside heating and cooling.
    No, it won't. But it will substantially increase the structural strength.

  9. #8
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    Re: Material and tube wall thickness for DIY travel trailer box?

    Quote Originally Posted by ezduzit View Post
    No, it won't. But it will substantially increase the structural strength.
    Well if the skin is stainless and the frame is mild steel the conductive heat loss will be epic. But sure, it will be strong.

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