How to keep CB magnet mount from scratchin paint?

I know this is an older post - but I have the same problem. However, knowing a little about ground plane and Antenna theory - it SEEMS to me [I am not an expert] that the metal to metal contact is important (!). That said, I understand the car paint is not metal - but it still seems an additional layer of cloth, cardboard, plastic ... will inhibit the efficiency. I have used aluminum foil - but was not happy as it weathered and marred that paint anyway. I'd like to hear from an old HAM on the effect of a non conductive material between the magnet and the car... maybe someone has actually measured the difference [in fact, I will post this to an Amateur Radio forum and return if I get some feedback]. Thanks!