Continuing to install little boxes behind the panel… this is a CO Guardian carbon monoxide detector, which I think is a worthwhile addition considering the cabin heat comes directly off one of the exhaust pipes. I made a little template out of some scrap aluminum to help me drill the mounting holes.
I attached the CO detector to the subpanel, to the right of the radio stack, with the screws on the forward (firewall) side. I was going to turn it around the other way, but there are too many things on the opposite side of the subapanel already and this is the only place it would fit.
Another view:
Here's a view from the other side, showing the mounting screws and the air inlet hole. It should be easy enough to get a screwdriver back under there to take it out every now and then – the sensor has a limited lifetime and has to be sent in for periodic replacement every few years (5? 7? I can't remember).
After I finished taking these pictures, I removed the CO detector and put it back in its plastic baggie to prevent drill chips from falling down into its little fan. Still a lot of construction going on in the vicinity.