rubber roof cleaning

My instructions suggest Murphy's Oil Soap or Spic and Span. I've also used the commercial roof cleaner from the RV supply. To be honest, none of it really works magically. I've owned three RVs and none of the roofs have stayed sparkling white. I clean them twice a year and rinse them thoroughly every time I was the unit. In the South, the humidity is high and the trees drop sap and the roof will develop the black moldy stuff. My neighbor used bleach to get his roof white again, but I think bleach is way too caustic. It's bound to cause some ill effects.