No question the roof is the heart of the RV, same as a house. Except that on an RV the seals and caulking require checking on a regular basis. We purchased our 2014 Sun Seeker in 2015, used and because it had been sitting in the sun over the hot Okanagan summer there was a large crack around the sky light on the dining room slide. Some mineral sprits for cleaning and Dicore fixed that issue. There was some deterioration around the front of the cap and same issue. Biggest disappointing thing I found was that none of the screws down the sides of the fiberglass roof , on the top of the moulding had never been covered over with Dicore. Apparently some of the units that left the factory did not have these screw heads covered over. (about 60 of them) , 30 on each side of the roof.
So the moral of this story is to get up on the roof and carefully look it over for even the slightest deterioration of any seams , roof vents, sky lights and all. I must admit even with Maxx Air covers over all 3 roof vents , which, need to be taken off and cleaned every 6 months, inside, the sealant can deteriorate and dirt builds up under them.