Dicor lap sealant or Eternabond tape for new roof vent

I would use Eternabond if it is possible. I've got Eternabond around everything on my trailer roof - but when I replaced the Fantastic Fan with a Maxxair Fan in my class B - couldn't use it. I don't remember for sure, but it had something to do with the mounting bolt heads - I think they were too big and high - so the Eternabond just wasn't working. Dicor worked great in that instance.