For me, it would depend on the quality of the fiberglass roof installation.
It could be a quality, professional job.
Or it could be something done by a group of guys drinkng large quantites of beer who decided to put a new roof on the RV one afternoon.
Tell your friend to have it inspected by soemone who repairs boats or other large fiberglass products.
The big question would be why it was installed and when. Did the original roof fail and leak? A new roof isn't much help if the walls sre rotting away from a previous leak.