http://www.stormcam.org/magnetic-mount/
How do I keep the paint from discoloring under a magnetic mount CB antenna?
The paint under my cb antenna always turns cloudy. How do i prevent this?
You might look into an extremely hard protective polish for your car. The high-tech coatings, like those used on aircraft, would be be best. It will probably cost you a few dollars in the beginning, but will protect your investment for years.
Here are a few links to browse; perhaps you can get some ideas.
http://www.hyperpolish.com/
http://www.fineautocare.com/
http://www.autogeek.net/
http://www.caswellplating.com/aids/collinit.htm
VORTEX STORM CHASER ™ MAGNETIC MOUNT ANEMOMETER