LTR, if you ask a dozen of us how we maintain the roof, you'll get a dozen different answers. Take notice of what everyone advises, and form your own procedures.
On your rig you probably have close to 100 feet of seams where the roof meets the sides and where it meets the front and rear caps, and where everything is attached to or pokes up through the roof. All need to be checked on a regular basis, and maintained. A small 1 inch gap can let in a lot of water.
I get up and give the roof on our Lexi ( fiberglass ) a good cleaning at least twice a year. I just use auto soap, bucket, soft bristle brush on a mop handle, and just scrub it down. Crud Cutter takes care of the nastier stains. I do not wax as I'm up there to much, and wax will make it very slippery when wet, and its a long way down.
I also, after each trip, get up there and spray off any leaves, pine needles, ect. that have found there way into all the nooks n crannies around vents, ac unit.
As for checking the seams, and repairing any cracks in the caulking, you can put new caulk over old, IF ITS CLEAN. Caulk will get dirty over time, and cracks in the caulk will eventually let water in. I clean the old caulk with mineral spirits, let it dry, and then go over it with acetone which gets rid of any residue.
Dicor is probably the best stuff out that is readily available. Two types, lap sealant which is good for vertical surfaces, and self leveling for flat surfaces, like around the vents, sunlight, fridge vent, and edge seems.
It is a bit of work, but if you want a leak free rig it must be done. There is no such thing as "maintaince free" when your talking about rv's