I had fiberglass deck covering for over 30 years, it got incredibly dirty & nasty so I replaced it with polycarbonate. The problem occurred the first heavy rain (I live in Oregon valley), the deck wraps around the house & detached garage, so there is a metal valley that runs from the roof & washes the water over the deck cover to the gutter. Although the connection of the fiberglass to the metal flashing was not an issue for 30 years, the connection of the polycarbonate to it was. The summer sun heated up the metal flashing (naturally) and caused the polycarbonate to deform and water just poured from one angle under the poly to the other side of the poly and under the deck. It looked as though it wasn't even covered. I was thinking of putting EDPM white over the metal flashing to protect the new poly from heat transfer. Thoughts?