On my Fleetwood I had rubber roof, who had some damages and age as well.
I tired all kind of expensive coulks on it and none of them really hold.
PO put eternabond on some damages, what in result channeled water on camper frame.
Finally after struggling with it for few years, I found new technology Henry Tropicool roof sealer at Home Depot. That stuff sticks to everything and HOLDS.
I used it on my house flat roof before going to camper.
The sealer will not fill heavy gaps, but 2nd application did the trick.
It is self-leveling, so hard to apply on sloping nose.