Three basic options here, one of which may not be available. One is factory replacement striping, which Winnebago may or may not have available for an '04. They generally do not produce more kits after the original production run of striping kits is sold out. Call and ask about yours. Option two is to have replacement decals fabricated by a vinyl/sign company, either an exact match or some alternate design. Option three is to have a Rbody shop paint the design on rather than using vinyl decals. All of these require a lot of labor to remove the old stuff first and clean the surface to receive the new. If you can do that yourself, great. If not, you are talking big bucks to pay somebody else to do it at a $100+/hour shop rate. It's many hours of hard labor, so think thousands rather than hundred of $.
At a guess, you are talking $4000 or so for labor and materials unless you do the removal yourself.