Flour board protection

[breb]

Slow I thought of tin ( or sheet stock) on the bottom side at one point but also afraid of trapping moisture in between. If there were a sealer and finish I'd be more apt to try something like that . Even my worry about a rock shield on the drop box on my build. I still wouldn't just screw it flat against the ply and mine is all finished with the mix and the rolled rubber roofing. Your area of the country is surly tougher on the bottom side of the trailer and probably would benefit from a tougher bottom like that. I think of a boat that is made of wood and fiberglass . The wood is it's form and structure and the fiberglass it's strength but the number one failure is the rot within the fiber glass. It does't allow the moisture to escape.