When we got our Fantastic Fan, it was recommended to use butyl tape instead of the foam sheet material that came with the fan. That stuff might work if you have a perfectly flat roof. I did overlap the ends and cleaned up the butyl tape that oozed out after a few days. It nicely oozed down into the gap when seen from the inside of the Boler
. It's been really hot here and I think that helped.
We've had some heavy rains several days right after fan installation and there was no sign of leakage.
I bought another 13' ft multi-use ladder (the ones that you can adjust and fold into several different configurations). That really helped during installation because I could quickly work on both sides of the Boler
without having to trundle the ladder to the other side. And it allowed me to reach over the centerline of the roof easily enough and maintain my balance safely despite my short arms.
Hope this helps....