I apologize if this comes off as a negative criticism, but I would not use foam as a water barrier. I would think it would do the exact opposite and attract water. The originals were some kind of waxed paper/cardboard? I got repros from Ames and they were a heavy mylar. The mylar or plastic repels the water and does what it is supposed to I guess. For economy even a heavy trash bag split in half and sealed around the edges may be a better choice.