Mounted the house heater.
First, VHB and screw down a riser.
Then measure 25 times to get enough confidence to drill the burner vent holes.
Whew, the holes and heater align!
Goop up the vent cover with lots of caulk. Mainly building up enough to fill the curvy part of Annie's wall. Screw it in nice and tight.
Cut the excess caulk and paint it silver to match Annie.
Screwed the heater to the riser, and we're done.
This marks (or almost marks) a milestone. I don't think there are any more openings to cut into Annie's driver side wall! I need to find out from Airhead if I can run the composting john's exhaust vent through the floor, instead of high on the wall, or through the roof.
If I can, here is Annie's complete left side.