I mounted one of those vertically in the rudder about 4 inches FWD of the aft edge of the rudder. I notched the ribs to make the ante a flush with the rib surface and glued it in place. Of course do this before covering the rudder. I ran one piece of coaxed from the radio to the antenna. A 4” round access is necessary to connect the coax to the antenna.
My plane only has 10 hours on it but it works good both in the air and on the ground. On the ground I can clearly hear another airport 50 miles away with mountains in between.