I've built trailers. You don't need much for carrying a few boards, whether it is practical is another mater for you to judge. People trail canoes, so SBs ought to be OK. Northern Hydrolics sells spoked wheels for thick axels, so does Lee Valley in their gardening section. You would need an axle, and then the towbar.

http://www.tolotrailers.com/

They appear to be using the wheels I mention above, though you could use BMX retreads. The frame here supports both sides of the axle, and is of a comon type. This does not require the heavy axle.

http://www.efn.org/~equinox/