If white, remove from RV and spray with a bleach containing bathroom-shower cleaner like scrubbing bubbles. Let soak, rinse off with pressure washer. Use magic sponge on any remaining spots, and replace. Protect with a plastic/rubber/vinyl protector like Meguires #40.
For black, Stonerís Trim Shine or Meguires Ultimate Black should restore the black sheen after washing.
2014 F150 SCrew 4x4 Max Tow Heavy Duty Payload 3.5 Ecoboost 6.5' bed Ingot Metallic Silver
2015 Rockwood Roo 21SS