Darin, I like the first one of Phil's the second not so much.
The trailer I would like to build would have a hinged top. I am not camping in it just using to haul my camping/ fishing gear. I was thinking along the lines of using front motorcycle tires with custom axle. I could even cover the wheels with something to make the rim entirely enclosed, and also do a full belly pan on the trailer.
I was just thinking the motorcycle rims/tires would not add much RR. The weight of trailer fully loaded would probably be somewhere in ballpark of 400-500lbs. If not even lighter.
Single wheel trailer from doublehitch.com I like that idea, would be cheap to build. Also easy to aero mod taper the rear easy with only one tire.