I think it has to do primarily with exposure to the sun. We have a 5er that was parked for several years at a campground and owned by the CG's owner. It was never waxed or covered, as far as I know. One side was in shade most of that time, and the other was exposed to the sun. The sunny side graphics are fading, cracked and peeling, while those on the shady side look almost like new.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.