At least once a year...
My Coleman is parked right next to my back porch and I can see the top, so it gets a once over every time I walk out the door.
Parking it under a shelter will help prolong the life of the sealants too.
It is a Dicor roof (I believe the membrane is actually made by Carlisle Syntec) so I would use the sealants they recommend. I would steer away from silicone on the roof. IMHO it doesn't work well for those applications. There is a another type of sealant that works much better and is a urethane base. Have to go find the tube, but it was suggested to me by a Master RVIA tech that has been in business for himself for the past 15 years and has a helluva good reputation.