Thanks guys, I got 1/2" CDX ply and painted it heavy with the same grey oil base machinery enamel, it's Ferguson grey to be exact. Thing wieghs 700# on the scales at the local sand and gravel place.
Still need to put longer saftey chains on it, put another tailgate chain on it, and if I get really carried away a folding ramp to the tailgate. I don't want the normal long tailgate/ramp commercial trailers come with, those things are like sails when you tow them, but it would be nice to be able to fold it down and drive a lawnmower or ATV up in it.
I have about 325 bucks in it now, all told.