by KCStudly » Sun Jul 12, 2015 10:27 am
I take it you are talking about slabbing wood onto the outside of the trailer frame main rails flush to the existing tops, then building your floor on top. Another option would be to build the wood rails as cleats added onto the floor and then drop the whole assembly onto the trailer frame. So long as the galley and front wall bulkheads cross and are supported by the steel trailer frame, the cabin structure will hold the floor up just fine. Remember, the unity of the cabin will do more to strengthen the steel frame, than the steel frame will do to strengthen the cabin. The cabin is a deep structural box section, whereas the trailer frame is a "floppy" wafer (relatively speaking from an engineering perspective).
All of the usual weather proofing comments need to be inserted here. Seal the wood really well with epoxy, or "the mix" (50/50 poly/mineral spirits) and exterior paint after you drill the holes for your fasteners (soak the holes well with the mix, even to the point of taping one side and filling the holes up and letting it soak for several minutes). (I am not a fan of the black gooey stuff.)
If you do decide to scab on wooden rails, consider using some small standoffs to space the wood off of the steel, maybe well treated squares of 1/2 inch ply, so that moisture is less likely to be trapped between the wood and steel; but then again you will need to look at your overall width to be sure you aren't making a lot of waste when you get to your ceiling and roof panel spans/stock sizes.
Consider using 1x3's or 1x4's instead of 2x4's The strength comes mostly from the installed depth, not the installed width, and you need to keep an eye on tire sidewall clearance.
I am of the school of thought that builds the cabin in the shop and then marries it to the trailer. I like to build as much as I can on the bench and then assemble. I feel it is easier to build this way and am not concerned with skirting or trying to hide the trailer frame (which could still be done). You could do it either way, or mix and match. In order of my preference; incorporating the rails into the floor of the cabin and then placing the assembly (allow a little clearance between wood and steel rails and don't bother fastening them together); scabbing the wooden rails onto the steel and then placing the built cabin on top; or stick building on top of the trailer and having to work around it while climbing in and out building a ship in a bottle. YPYMYTYC (you pays your money, you takes your choice).
KC
My Build:
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Poet Creek Or Bust
Engineering the TLAR way - "That Looks About Right"
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