Conduit tubing is pretty light. And there are devices to bend it. What about hardware cloth for the bottom? It's a wire mesh (about 1/4 inch square), less stretchy than chicken wire. Depends on how much weight you want to put in the bottom of the trailer, but you could add some cross-braces if necessary.

A trick I've seen on Burley trailers to increase their stability is to dish the wheels towards the outside, widening the wheelbase without widening the trailer.