Help! we have a 2007 Wildcat 5th wheel, bought it used 3 years ago. Just this year, all of our exterior side of all the storage doors have turned yellow!!! I have tried different products to try to make them white again but no luck! Hoping someone out there might have a trick up their sleeve as we want to sell this one in the next year to get a newer one and don't really want to have to replace all 4 doors!!