I went to Home Depot and got a 4'x4' chunk of Plumber's Vinyl that they use under shower stalls. It's about 40 mil, liners are usually 20-30 mil, very smooth, and keeps the wedding cake steps from abrading the liner. I've been using it for 8 years now. I trimmed it to be approximately the shape of the steps and slightly larger. If you have an old liner that you use for patches you could use a chunk of that. The Plumber's Vinyl is gray and has markings on one side--that side goes down.