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 ...
Just lightly spray the roof with spic and span or other soap and bleach mix. It really doesn’t need to be all that toxic to kill the mold. Use a yard sprayer. Use plenty of water to rinse which should dilute the runoff so damaging the lawn should be a nonissue.