Heres what I do. I have the plastic you can buy anywhere, for templates. I went to a business/ menards-Lowes, etc. I went and ask for a plain sheet of bathroom paneling. It a sheet 4 x 8 white, give or take 1/8'' in thickness. When I make the thin plastic template. I go out to my garage, and cut a peice of that paneling, a little bigger. And trim it down to what I need, when I go back inside. It works great for me. And everyone, else that have mentioned what they do, are great suggestions, also