We purchased 48" wide, 100% polyester fabric to use as peel-ply. It worked really well! This fabric is sold at any fabric store in the "linings" area. Had we caught it on sale, we could have purchased it for about $2 per yard.
1) Purchase a little more than 8 feet to do an 8' board.
2) When applying, either press out the center crease (with an iron and an ironing board) OR make sure the crease is pointing down (towards the board). We had it pointing up on this side of the board, which caused a small ridge to be created down the length of the board.
3) The lining fabric has a finer texture than peel ply. We're thinking that we'll have to rough up the surface of the board to ensure that epoxy adheres to it.