We have been researching transponder installation options for our
ASW-27B (carbon fuselage) and have seen or heard about antenna
installations on the bottom of the fuselage in front and behind the
gear ... on top of the deck ... and with internal or external ground
planes ... and without ground planes. All appear to work, although I
have not seen any hard empirical data or testing results that shows
one type of installation is marginal ... or another superior.

How about in the tail -- not carbon -- right next to the radio
antenna? It's certainly easier before they glue the fuse together, but
one might be able to get the transponder antenna in there after the
fact too.

John Cochrane