I used a commercial grade rubber type. It came in a large, heavy roll. Easy to cut with heavy duty scissors or a #11 blade. I cut it just slightly wider than the Fastrack and made paper templates for the curves. By using a "cookie cutter" approach I was able to minimize the waste. Leftover pieces are handy for shimming.
Ah. Great idea. I thought you covered the entire layout with it. Cuts down on the weight as well.