I'd like to know the answer too. Bleach works great for mold and mildew but I have dark brown/black spots mostly on the underside that nothing touches and I've tried just about everything I can think of.
2020 Silverado 2500HD LT, CC, 4X4 6.6 Duramax
2021 Grand Design Reflection 311BHS
I asked him to do one thing and he didn't do any of them.