Paints are Thermo-Plastic (acrylic) and heated in factory ovens. The Magnifying Glass Effect with acid rain may also heat the paint to those temperatures, softening the paint.

Acid rain may etch dull-looking spots into an RVs paint. Acids in rainwater don't evaporate but, instead, become more concentrated as the raindrops dry.
Heat from the sun or engine can increase the damage.

 
MAXXGARD is a trademark of Maximum Protection Systems