Roof maintenance

There are too many variables for anyone to give a good answer. Here is a few: Age of RV, Construction of RV, Stored outdoors or indoors, Local climate (Arizona or Maine), local conditions (sappy trees etc.)

I do it at least twice a year myself as our rig does sit in the sun uncovered most of the year. Most RV manufacturers recommend twice a year as well, I usually touch up suspect seams once a season using Dicor self-leveling from CW.