In the early 2000's this was a major issue with a number of RV manufacturers that purchased their fiberglass from Dow Corning. It wasn't just RV's as Corvettes also suffered the same issue. Around 2006 most of this was resolved and has not been as major an issue as it was before. If you check a number of the RV forum's you'll see reference to dark colors that are left exposed on a regular basis seem to bring about some checking. That said, my 2008 Discovery 40X was always parked outside year round an was the dark paint scheme, but never showed any issue with checking.

What I've read on the topic indicates the common causes if the source is localized is something having struck the surface and caused the undercoat to crack eventually leading to the surface paint showing checking. When it is not localized, the general consensuses is the repair to eliminate the issue is sand everything down to the fiberglass then prime and paint,  The other option is to actually replace the walls and paint. 

Not an easy solution, but seen across all manufacturer. I know of several folks with Winnebago's with the problem, and my son's Newmar Essex which is dark green has the same problem.

The good news, if you can call it that, is it is cosmetic and does not impact function.