Hi,
I have always used "Rubber roof sealant" on my rubber roof, there is no specific reason it will not work with a fiberglass roof. It is very elastic, and even sticky years later when trying to remove what I had installed a long time ago.
CampingWorld.com sells it, or perhaps your local RV dealer or parts department?
I replaced all my roof vents with Fantastic fans back in 1996, when my RV was new. They are still great! By turning them all on, and then closing all the windows except the one near the couch or dinette, then all the air must pass through there, and it cools me off quickly! I really like the one in the kitchen, it gets used a lot more than the noisy fan over the stove.
I was able to find 12 volt wires near each roof vent, pre-installed by Fleetwood in the Bounder motorhomes. You can remove the inside vent for any non-powered roof vent and look for 12 volt wires, many manufactures install them at the factory, so dealerships can install Fantastic fans afterwords to those who want them.
Mine do not have remote controls, that is a new thing they just started with. Good luck on your install!
Fred.