Nice! How did you fasten both cowls\housings to the ceiling? Looks like you used some screws or something to that effect. If so, did the screws go through the panel and into the mushroom? That's kind of the only part I wasn't clear on. Smart sealing out the stank from the panel.
The method for the hole though was kind of involved and I was in the zone and forgot to document it.
I found some PVC pipe that was almost the exact diameter of the airhead vent fan cowl piece, drilled a hole just big enough for the pipe to slide through in the roof, then coated the hole, pipe, Inside and outside with adhesive and let it set and seal.
This way, there is no air gap where the stank could possibly permeate Into the foam insulation exposed from the hole. Make sense?
I just used a round vent from a boat.
It’s nice and super low profile.
Here’s a link: JR Products 02-29125 Mushroom...