I maybe should do it more often as mine is in the sun always.
Also for some that see the above post there are lots of different types of roofs. Berkshires have a fiberglass roof and the rubber roof products should not be used in them.
We use the 303 on whitewater rafts. Best sunscreen out there for PVC. Don't overdo it though, as too many applications in a year will soften the PVC coated fabric used on the rafts. Not sure what the roof material is though.