Your profile shows you have a Pace Arrow. If that's true this question would probably get better answers if posted in the Fleetwood forum.
If you do have a Winnebago product please give more details as to the model. I do know the Adventurer and Chieftain series do have fiberglass roofs. I'm not sure of the other models.
There have been several posts over the years about using Eternabond tape on these roofs. Some results have been positive while others were only temporary fixes. One of the more recent threads was from an owner that had long term problems. After a few years the tape started to separate from the roof. He had a miserable time trying to remove the remainder and reseal the roof.
Personally I've never used the tape so I don't know if the related problems were from improper installation, faulty materials, or they just reached the end of their expected life span.
I do know that Winnebago recommends inspecting the roof seams every 6 months, and replacing sealing material as necessary. We followed the routine with our 2001 Adventurer. We even had the seams inspected by the factory technicians when we took it in for service. In the 12 years and over 100,000 miles we had it we only had to replace a couple small sections of sealant.
2013 Adventurer 32H