After spending way to much time on the net trying to work out where to put my com gps and transponder antennas, after many hours of wasted time I caved and just went with what I felt comfortable with. The comant bent whip has the same footprint as the gps antenna so I utilised the gps backing plate for the com and used the existing doubler/gusset for the gps.
I fit the com in the out board bay under the pilots seat
After much deliberation I fit the gps just aft of the rear window