I have a class A with a fiberglass roof. I park it along a tree line in the summer & inside in the winter The roof is black on about 25% of it. I got up there today with a bucket of oxyclean mixed ...
I use Tile X on my awning - seems to work - should work on the roof. Just spray enough to wet the moss/mold and be patient. You can do the same with spray bottle and a bleach/water combo.