I decided to install a GHA 15 and it made sense to do it before installing the cabin top. I chose to mount it just aft of the baggage compartment.
After looking at photos of landing aircraft, this location seemed optimal to me. It will also be easy to tie into the CAN bus in this location. I chose the left side as my CAN bus starts in the right wing, crosses the panel, and proceeds down the left side of the airplane.
I made a doubler and attached nut plates for the screws.
The sensor sits just aft of the tailcone seam. This location should hopefully work well.