Barrier Paper

I have a 65 Barracuda and yes they also had a vapor barrier behind the rear sail panels. In the Barracuda VERY important. I have intentionally left it in the rain a few times to find the leaks and I have to say a pretty fair amount hits the plastic behind the sail panels. I have had to adapt it a little because I have some wires coming out of mine.

I replaced mine with 3mil Plastic Drop Cloth. It is thick enough to handle the job it is made from the right plastic that will last through the heat and cold and it is cheap. I used the panels as a guide to cut out the plastic. And laugh if you like but I used clear caulk as a sealant. Honestly it does not need to be 100% water proof at least in the Barracuda because the water goes to the bottom and is dripped out of weep holes. You do need to make sure ALL water gets directed to the bottom opening and make sure the space between the vehicle panel and interior wall is completely clean.