I was in a similar situation last year, and opted to just mount the portable unit in the back & run the flexible tubing into the cabin. It takes up some fishing real-estate, and looks ugly, but then makes for no through-hull fittings. I place mine on my cooler seat in the back so the exhaust is high enough to blow over the side and use a ratchet to fasten it to the gunnel. It has its own deep cycle battery which lives with it, so no worries about hard wiring. Takes 5 minutes to set up, and just remove when not needed for a hunting/camping adventure. Mines a drop curtain, so I didn’t need to drill a hole.