Roof vent installation on high top van?

[TMG51]

I'm finally installing the maxxair vent on my fiberglass hitop roof.  Does it really matter if I use putty or butyl  tape?  I still have a lot of putty tape from when I installed the fantastic vent on my metal roof last year.

I used caulking. No leaks in over a year so far. I think the tape matters more when you have to build up any valleys. But then, I'm a rule breaker anyway.

 

[FreeAtLast]

If I had to cut the 14x14 hole new, I would mark it out, tape plastic hanging from the ceiling on the inside to catch sawdust (fiberglass is nasty), make 4 plunge cuts in the middle of my marks with a circular saw, and then finish the corners with a small tooth hand saw.

Experience is what we get when we don't get what we want.  Sure wish I had read this about a week ago.  I don't have a high-top and my metal roof is full of 'hills and valleys', but that's the best advice on making a 14 inch square hole that I've read yet.  Much better than drill the corner holes and connect the dots.  Don't ask how I know; just refer to my opening sentence.  Still working on how best to make it right.

Thanks again, TMG51.