PLEASE check (with whatever RV you buy) with the dealer and insurance carrier what you can and can't do to your roof. You can negate
your warranty if you use certain products on your roof. Read the paperwork if your've already purchased an unit or research online. Most rubber roofs are not to be sealed or have a protectant placed on them (by not sealing I mean the entire surface not the seams or around hatches, antennas etc, those you need to keep an eye on and maintain to avoid leakage.) Rubber roofs do have a long life and minimal upkeep is needed. Remember companies put EPDM on their expansive roofs and absolutely NO upkeep for a couple of decades at the very least. We get rather anal when it comes to RV roofs for some reason. Don't let your RV 'own' you, making you a slave to it's upkeep, as many product sellers will tell you you 'have to' use their product. Of course they do, they want the revenue.
As an aside, I agree that 303 is great for protecting plastic, rubber (tires and around windows etc) and decals (if you have them). Great sunscreen..just be aware of the area your RV will 'live' in...if it's places like AZ etc with extreme heat and sun, you will need to reapply more frequently. Great stuff for your vehicle/s too! I didn't put anything on my roof as the manufacturer's paperwork said 'No protectant on the EPDM' as it would affect the warranty, but I hand applied 303 to the gel coat on the sides of my 5'er.