There are a few different things that can contribute to black streaks on an RV. The primary cause is rain or water from an air conditioning unit.
Use a bucket of soapy water to dip a sponge or brush, then wipe the grime from the RV. You may have to scrub a bit to get the worst spots clean.
A large portion of RVs has fiberglass exteriors. But removing black streaks from a fiberglass RV exterior is the same process.
Camco Pro-Strength Black Streak Remover A company widely regarded for its dedication to the RV industry and consistently provides excellent products for RVs.
It’s also safe for fiberglass, metal, or painted surfaces and leaves most durable polishes intact.