Sweep the RV roof with a broom. Be careful not to sweep any dirt or leaves into the drain under any roof-mounted air conditioning equipment. Use a ladder to reach all areas of the roof and avoid damaging the roof's protective surface.
Apply a bug and tar remover formulated for fiberglass to any of the areas affected by bugs, tree sap or white or black streaks caused by roof oxidation. Bug and tar removers safe for fiberglass can be purchased at any auto parts store or an RV supply warehouse.
Wash the fiberglass with a sponge that has been dipped in a solution of 1 cup of liquid laundry detergent and 1 gallon of warm water. Start at the roof line. Re-wet the sponge often to avoid dirt transfer.
Rinse the detergent off by spraying the RV with a garden hose. Allow the surface to dry naturally.
Put on gloves. Dampen a cloth with MEK and wipe down the fiberglass with it. Start at the top and working down the sides. Reapply the MEK to your cloth as needed so that the solvent removes grease and oils. Methyl ethyl ketone (MEK) can be purchased at a large home improvement store, RV supply store or any paint store that carries solvents.
Apply a fiberglass wax by following the manufacturer's instructions. The wax will fill any microscopic pitting in the gel coat and restore the reflective surface.
