Here is an alternate technique to consider when designing a teardrop, a canned ham or a box trailer:
On top of the frame rails for the chassis one can weld square tube lengthwise (every 16 or 24 inches) to carry the plywood floor. The outer edge of this arrangement can be angle iron (3/16" thick with a leg hanging down perfectly covering the open holes of the square tube). Weld the square tube cross members to the angle iron. One can then carriage bolt the wall plywood to the angle iron, caulking before bolting in the contact area. One can then lay the floor and bolt it down with carriage bolts through the square tube, caulking all the contact area and the edge that meets the wall. One can build the insulated walls in place on the trailer, putting the roof on last.
One could use the same square tube for the outer edge instead of angle iron, but it's not necessary and adds more weight.
Using this bolted walls method not only guarantees that the walls are absolutely integral with the chassis for strength, but you don't necessarily have to have a shop with a big table or floor to build the walls. You can just build in smaller increments directly on the chassis, AND without needing lots of help to lift pre-built walls into place. (See second blue link below for pictures.)
