It all looks so nice that I plan to rob most of your ideas. Honestly, I started creating a design and then found the Trailer Talk thread and had some of my ideas vindicated. I like your build a lot. You said you were going to use 16 gauge for the outside. Are you going to cross break it or you going to put anything on the inside for support, like ply wood? Also, how are you going to fasten, weld, screws, tape?
My idea was to run some sort of seal on the skeleton and bolt the skin on with nutserts and stainless bolts. The fasteners will break up the long panels a bit and I really want it sealed and i cant stand rattle noises. I also wanted ply wood on the inside for a "warmer" feeling for the cargo. Plus it will be my dog house when i piss the misses off on the trip.
Keep up the good work.