When I was battling leak(s) on my new Scamp, I suspected the VanAir bathroom vent / fan because there was a gap in the sealant.  So I took it out and reinstalled it.   Once I got it out, I saw that the original install used butyl tape and looked to be a good job, and I later found different holes in the roof that were in fact causing a leak so in sum, I think my bath vent was not probably leaking after all. 

However the vent is held in place with screws into the fiberglass roof.  Look at these photos and decide for yourself if there is a concern.