Welcome to the forum.
Actually Dicor makes some stuff to fix or re-new rubber roofs. I have done this on my old Kountry Star I had and recently on a Thor "Park Avenue".
It is a two part process. (Three step) First you clean the roof very well with something along the lines of Tri-sodium-phosphate. That is to get all the old oxidized rubber roof stuff off. Then you clean it with a mild cleaner to make sure to get all the TSP residual stuff off.
Then after it is completely dry there is a "Primer" coating you use. This actually softens up teh rubber roof chemically so the next step in the process will chemically bond to the old rubber material.
Then the final step is to put several coats of the rubber roof coating material.
It is best if once you get the roof all cleaned to do the final two steps you move the rig into an enclosed area or at leat a covered area. This is to keep trash, bugs and the like from getting into the stuff while it is drying.
I also removed the Air Conditioners and refrigerator vent while doing the ones I did. Then put a new gasket under the A\C when I re-installed it.
It takes a lot of time and elbow greese to do it right. But when done you more or less have a new roof. The materials are not cheap either. I would have to look up the names and prices if you are interested. But on the Park Avenue if I remember right the total cost of materials was something like $150.00 to $200.00...... If you were to pay someone to do this it would be very costly due to the time it takes to do it right.
Hope this helps ya.