waterproofing underside of cabover

I used 3/4 exterior ply for the floor and applied 3 coats of deck paint to all surfaces. For the skin I used 4x8 sheets of fiberglass from a builders surplus store. This is the same material used for the wall of a shower stall. Cost $12 each. The advantage in my opinion of the fiberglass sheet over laminate is the flexibility. You're not going to get the laminate to wrap around the nose of the overhang if that's what you need to do. And, it's waterproof inside and out. When working with the fiberglass I used 1" 3M VHB tape to adhere it to the frame then instead of re-installing the aluminum edges I used 3 layers of 4" fiberglass tape and MAS epoxy (used in wooden boat building).