Winnebago Vista 35F

I'll say this and then let it be; A roof, fiberglass or not is not the largest concern. All roofs have seams and holes and that is where leaks come from. I would guess that very few leaks actually are from perforations in the membrane itself. It's from a seam or someplace that a component is attached. Also, if TPO, that's an easy and cheap fix. Fiberglass, not so much. I have seen the thin skin of fiberglass that Winnie puts on. It's not by any means impervious. Might be stronger than TPO but I wouldn’t guess by much. I like this quote from Dicor Pres Gregg Fore, “The fiberglass used on roofs is so thin that if it gets stressed in installation – which you may or may not know about – it can develop hairline cracks because of its stiffness,”

IMHO,, the largest deciding factor with any new or used MH is floorplan, then reliability of all the components.