No matter what type of roof you have there is the same number of cut outs for vents, AC's, skylights etc, this is where leaks occur. I have a 24 year out MH with a rubber roof(EPDM) it has never leaked through the membrane. I recaulk and inspect at least once a year and never had a roof leak. I have resealed most of my windows due to water leaks because butyl rubber tape dries out. I have seen MH's with FG roofs with a lot of water damage because caulking cracked and water got in. So I would be more concerned how the roof was maintained rather than the material the roof was made of.