I bought one of the factory made steel tub trailers. It's pretty heavy but nearly indestructible. I've bouced it and flipped it and had it pop off the hitch fully loaded and I just hook it back up and keep on going. (I keep the hitch a little loose on the ball so it will pop off under stress rather than twist the hitch). I put a tarp over it and run one long home-made bungee cord around the rim to seal it. Then I put a big cargo net over it and run a few more straps across the top. I've flipped it over in creeks without getting any water in.
I had some ideas to build my own but the materials and labour would have cost me more here. I thought if you could get the front half of a broken plastic canoe, then goose-neck the hitch bar, you'd have a trailer that would never hang up. It would be tough, light weight, quiet, and would slide over anything.

 

I'd design a trailer that hooked up and loaded itself!