Top layers of ply sealed on the inside, then glued and screwed down. The base is amazingly strong and fairly light. I'll let it cure for a couple of days now, since temps will drop into the 60s. I'll then sand it all, seal it completely on the exterior with a 3 step polyurethane mix. Poly: Water 25:75, then 50:50, then 75:25. After the poly fully cures, I'll then cover the bottom with cool seal, flip it back over and through bolt it onto the trailer frame. Yippee, almost done except for the finishing. :-)