Rubber roof cleaning

Was just wandering how most of you clean your rubber roof. I generally
Get on top of mine at the beginning of camping season - mid summer and
late fall. I usually just always use Thretford rubber roof cleaner and a scrub
brush. Even though our camper is always under a camper awning, the roof
still gets very dirty. There are several places that has what looks like little black
mold dots that are very hard to remove. I only want to use products that want hurt
or remove the wax finish off the fiberglass. I didn't know if a electric pressure washer
would help or could harm the roof - that in itself could be a chore to get on top. Just
wanted to see what most folks used to keep their rubber roof looking new. Thanks and
happy camping to all.