I have my VOR/ILS antenna on the top of the vertical fin. I obtained piece of square tube (approx 3/4-1” square not sure), mounted it to the top rib under the tip. Then mounted the antenna to the tube. This way the antenna is raised up a bit so you don’t have to cut the flange off the the top rib. It is all well concealed except for the rods sticking out which shouldn’t be much drag as they are swept back at about 45 degrees. Works perfect.
O-360-A1F6 (parallel valve) 180HP
Precision F.I. with AP purge valve
Vinyl Wrapped Exterior
Grand Rapids EFIS
Located in western Canada