How to keep CB magnet mount from scratchin paint?

Further explanation, attempting to keep this in some context that you can visualize.........The mag mount must 'ground' to the car body, for lack of other.........by capacitance. Capacitance is effected, at least in some ways, by the thickness and type of insulation (dielectric) between the two plates of the capacitor---one being the car body, the other being the metal on the bottom of the mag mount, by the distance such as other objects such as plastic film in between, by the diameter (surface area) of the plates (the mag mount)

This works like a coupling capacitor, which are used to couple AC signals. An example might be an audio amplifier. Modern microphones often are powered by DC power sometimes called "phantom" power, because that power is sent down the mic cable itself. BUT INSIDE the amplifier, going to the input stages of the pre-amp, this DC power must be BLOCKED from the amplifier circuit, so a COUPLING or DC BLOCKING cap is used. The value (size, capacitance) must be tailored for the audio frequency range. This coupling cap, then, "feeds" the audio AC signal from the mic cable to the input stages of the amp

What we are dealing with here is RF. Just like the coupling cap above, the capacity of the mag mount is much MORE effective at RF coupling at VHF, and better yet at UHF, than it is at lower, HF frequencies. This coupling, called "capacitive reactance", or Xc, is the AC equivalent, so to speak, of RESISTANCE value of a resistor. This reactance varies with many things in a circuit, as well as the frequency of the AC signal, in the case of CB, of course, about 27mhz