I used 1/4" construction grade ply, and aluminum channels for edges and corners. It required some internal bracing. I wanted access when the boat is on the trailer, so there are doors at both ends and a sliding hatch on top at one end. This has not proved entirely satisfactory, due to leakage, but a cheap tarp from Lowe's has solved that.
Last edited by pgp; 01/09/10 09:46 AM.