I decided to go with the measurements I have, they look close enough
for the cross members I used a sheet of .080" cut to 10" scale then cut them into 2' scale for the outside cross-members that go on 1,3, and 5 cross-members.

When you glue the two together they come up with the thickness I figured they need to be which is 6" scale, cause evergreen, or plastruct neither one make a cross member to fit, so you haft to make all of your own, which is no big deal.

The only problem when you cut that 10" off the sheet I got, that makes enough outside cross-members for 2 of the cross-members, but I need them for 3, so I'll haft to find use for that remainder of that 10" after I get the next 2 cut off it.

Now I got to find something to glue together to make a scale 4" to make the main beams, why the crossbeams would be 6", and the main beams be 4", but of course they are 14" by 4" wide though to in scale, where the cross were 6"by 10".

I ended up using .020" for the floor, and cut it off at the angle for the drop going down in the back, then I cut out the center like it is on the trailer, so the bottom will be supported by the beams in the back, and the front will be supported by the beams on top.

But the floor cut and the side beams cut and glued together, then shaved to size, all but 2, and that is it so far, I wished I had a camera, maybe some day. I figured out 2 .060" glued together will give me my 4" by 14" main beams so that will work out fine to.
Kerry