I've got my new blind almost done. It is 4X8 with a flat 8x12 roof which is composed of 3 4x8 sheets of marine plywood. I'll caulk the seams and reinforce it but I WAS going to just lay a sheet of rubber or something over the plywood. Looking at the prices that stuff is expensive!

What would you guys (gals) suggest to lay over the plywood roof to keep the rain from coming through? Let's use $50 as a maximum cost or thereabouts.

And I really appreciate any help you can give me!

(I didn't take any pics but this blind will be the "mother" of all luxury blinds)...