Back when I was working to figure out how to build a trailer, I had a Chariot Fiberglass enclosed and it was AWESOME! Strong, light, weather tight. Although it could be a bit of a bear to work on as far as modifications go.
Anyway. I was researching and going through some stuff and came up on this:
http://www.boardlady.com/trailer.htm The lady's name is Eva Holman, she is quite well known in sailboat and sail and kite boarding circles. The link shows a trailer that she built from scraps of other projects she had laying around.
It's strong, light, easy to tow and cheap.....
I am still kicking around the idea of doing something like this.