Fabricated a .032 doubler for the COMM antenna and found a position to mount it on the passenger side belly, inboard of the Dynon roll servo bay. Still gives sufficient distance between that and the transponder antenna. Spoke with Dynon about the transponder, and Dynon radio at CopperState fly-in. Both have 'control on the instrument panel' but remote components with RF energy. Decided to following the suggestions and isolate the RF (coax, and radio components) under the seats, and shorten the length of coax in the cabin.
This was my daughter's first opportunity on the bucking bar. Not perfect, but hey it's on the belly --- Will mount the antenna later. Transponder will get a minimal doubler, when ready to drill the hole.