Not sure how long aged graphics might be to get off but on cars etc a hair dryer and a lot paitence and pulling and peeling possibly.
A Good RV Service Center may have dealt with this many times.Certainly the factory has. Call the factory and try to speak to a tech in their service department...unless you don't care and are going to trade it etc.If i could I would paint on new graphic of your design or copy the decals,if the pint or fibergalls finish is still good.