Another option is to install the antenna on top of the fuselage just behind where the cockpit vent exhaust would be. I think it was Andy Durbin that posted many years ago that he did some research which involved talking to people actually involved in building ATC radars, and the consensus was that the top of the fuselage is just as good as the bottom.

Install a pretty blade antenna on top and paint some cool lightning bolts on it, just put a sticker like this on it:
http://static.seton.ca/media/catalog...s-s2283-ba.jpg

On Saturday, March 5, 2016 at 1:21:09 PM UTC-8, Darryl Ramm wrote:
I'm not sure why all the complex approach of vertical fin mounted transponder and FLARM antennas is needed in the first place. The transponder antenna behind the gear door works fantastically well, is really not a hassle unless you are stupidly careless.. and then it's easy to replace anyhow). People are getting good performance of FLARM antennas mounted in the cockpit area, including the nose cone area of ASW-27.