I started using Glad Press n Seal a couple of years ago, and find it to be an excellent masking medium. It takes a little getting used to, but is easy when you get the hang of it. Burnish it with a toothpick or similar tool, and cut it with a sharp exacto blade. It's deffinately worth a try, and relatively inexpensive to boot.
Note- It will leave a residue if left on for several days or longer. If this happens, the residue can be removed with polish.