Mich F wrote:
Sure plenty of people have water leaks, but usually at transition points, like roof to wall, or around windows and vents and such, not through or because they have a rubber roof. In all those cases it doesn't make any difference whether the roof is rubber or fiberglass.
Probably the transition points between a smooth fiberglass roof and plastic vent edges, metal A/C bases, plastic bathroom skylight edges, metal antenna bases, etc., are easier to seal (using Eternbond, self-leveling sealants, etc.) than trying to get some material to adhere to porous rubber in those transition areas.
Also ... regarding even RVs with one-piece fiberglass roofs ... I wouldn't buy one unless the fiberglass roof also had rolled edges all along each side (in addition to a nice crown). Rolled edges eliminate another two-times-the-roof-length of leak prone seams.