Had the same problem with black decals. Sun stroked for lack of a better description. The low to no cost but lots of labor way is using a heat gun and a plastic putty knife. A bit of mineral spirits helps with any residual glue.
The fast way but will cost a bit is an eraser wheel in a corded electric drill. https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
. I used heat on one side of the coach and it took all weekend. Two wheels on the other side and was done in an hour.
For the sun damaged gel coat I've tried buffing, Mcguire's miracle something or other, Polyglow, Turtle stuff, NuFinish (paste and liquid) and nothing seems to last longer than a two or three months on gel coat fiberglass. I broke down and pulled the nuclear trigger used Zep and haven't looked back. The coach is a 2006 and is out in the weather 24/7 parked out in the sun, rain, snow, wind getting full morning and afternoon sun as seen in the posted image.
BTW the red striping used to be black decals. Replaced with paint.