Welcome to the forum bob57434.
Can you tell us a little about the RV? Did you get it recently or have you had it a couple years?
It sounds like someone coated the roof but, didn't clean it properly before applying the coating.
There are recommended coatings for RV roofs. Automotive under body sealant isn't one of them. You shouldn't use anything containing petroleum, it can damage the rubber.
I wouldn't use the floor epoxy. There are truck bed liner type materials used for RV roofs.
For repairing rips or tears in the rubber,
Eternabond is an excellent product.
Also,
Dicor Lap Sealant for the areas Eternabond is difficult to apply.