I put the pad inside my bag and use a bag liner from sea to summit. I really like this combination and I can add R value to my bag. Using a Klymit KSB 20 synthetic bag with a sea to summit liner and a Thermarest Prolite.
I have two small rectangles of the mesh style rubber tool box liners cut to 18" by 24". I use these for a great many things in and around camp as well as to wrap certain items in my pack. At night I place them between my bag and pad to keep me from sliding around. You can get this stuff in big rolls from Sears, Walmart, Amazon, etc.