We store ours under an awning at a storage facility, so the roof does not get direct sunlight except when we are using it. We use it every month of the year over a long weekends and a 1 or 2 week vacation. After washing the roof, I apply 303 to the entire roof, including shrouds, antennas, etc, except for the solar panels.
I had my first RV for 5 years, and the roof looked new when I sold it. I bought my current RV about a year ago, and I’m just about to use 303 on the roof for the second time.
You can see my RV and read about some of our trips here:
http://mobilemosers.com