Here is my notes from about 5 years ago.
If you rub the fiberglass with your hand and get white residue on your fingers, you definitely need to clean this oxidation off before polishing or waxing.
Go to the auto parts store or a marine store and get either some "3M White Scotch-Brite cleaning pads" or the "3M gray super fine pads". Don't use the more abrasive Scotch-Brite pads or you will have to end up wet sanding the scratches out. The gray pads are finer than the white and do a great job.
The gray pad is better for cleaning the oxidation off the fiberglass but the white pad is better for removing adhesive stains and tar. It is also better for cleaning off old wax. The white pad can be used with a lot of solvents that destroy the gray pad. A little lacquer thinner will make short work of adhesive marks or road tar. Using the white pad with a muriatic acid solution will take up rust stains. Be careful though. Solvents that don't hurt fiberglass can damage paint
, decals, and you. Take precautions. Also, after using solvents, flush with water and clean with the gray pad.
Start at the top with the hose running and start rubbing the pad in a circular motion under the water. The water turns white. Move when the water clears. When everything dries, it should be easy to tell if you missed anywhere. Use a pencil to lightly mark the areas you missed or need to clean better and go over the areas you missed. The pad will take off the pencil marks. All this is a little time consuming, but, it isn't very hard and you can do it out in the sun.
Polishing and waxing after all that chalky oxidation is off is now a piece of cake.
Polish (for cleaning and shining dull spots): Starbrite Marine Polish
Wax (for protecting): Meguiars Flagship Premium Marine Wax
If you have a pressure washer, DON'T USE IT AROUND THE DOOR, WINDOWS
, VENTS OR ANYTHING WITH A GASKET. It will blow out all the silicone caulking. In other words, it isn't worth renting a washer or going to a car wash. Use a hose.