Welcome to the forum. We have a search feature located in the blue bar at the top of every forum page. Click on search, then type in "decal" or Graphics" and you'll get a "ton" of information regarding this issue.
Here's one to get you started:
http://www.keystonerv.org/forums/sho...ighlight=decal
Other than shielding them from the heat and the UV rays, there's not much you can do to prevent the "next set" from doing what the "current set" has done. As to the current condition of your graphics, there's not anything I'm aware of that will "rejuvenate" the damaged decals.
Again, welcome.