We have been lucky here in the great Northwet! I keep one of THESEgoing all the time and also keep a vent open or window slightly open. So far no mold! I also do not cover our 5th wheel. A little more information might help others in suggestions! i.e. where are you located, is your RV covered, do you have any type of dehumidifier, was there ever a water leaketc.
More info where is it??? If its from moisture inside the RV the open windows and vents from now on to keep it to a minimum. If an outside source you will have to find it and seal. As to clean up ZEP from Home depot does wonders, I use it in my rentals to kill and get rid of the mold. And then the ZEP bathroom cleaner to clean it. Stinks bad so spray and run, then as it settles scrub lightly with whatever is appropriate and rinse.