Installed the ADS-B antenna this morning by drilling out a 1/2" hole below the passenger seat (through the right wing spar bolt access panel) and routing the antenna cable to the antenna. Besides drilling the hole and tightening the antenna to the aircraft skin, I trimmed the antenna cable, added a BNC connector to the end of the cable, and riveted in a couple of cable tie mounts (1 to the wing spar upright and one to the cabin floor) to secure the antenna cable.
Looking down from above: ADS-B antenna seen through the passenger seat access port.
ADS-B antenna cable running down spar upright across floor under seat.
ADS-B antenna protruding from the underside of the aircraft.