My 5ver sits in the yard for storage. out od necessity the same side of the trailer has faced south since July 2008. The darkest decals/stripes have begun to shrink and crack, making bright white lines in the almost black decal.
The lighter decals aren't doing too bad.
So since I am the really cheap sort, I just painted over the cracks with an oil based paint pen from the local craft store. While the results are not exactly factory finish, they suit me fine. The camper is nearly 10 years old and is in pretty good shape, but does show signs of being 10 years old. At least you don't notice when looking at the trailer from the next site over.
The craft store lady will try to sell you a fancy magic marker every time. No. It must be an oil based paint pen.
And when you're done touching up the decals you can put your name on your LP tanks.
On edit: Trust me, it looks way better standing there than it does in the pics.