antenna

Hi all, I decided to mount my transponder and ADS-B antennas inside my Kitfox 7SS. I'm trying to prevent them from getting snapped off if they protrude from the bottom. I built a ground plane mount to attach to the steel tube fuselage, but Id like to get some input from you out there...

The best place to mount the transponder antenna in my airplane is the aircraft skin under the seat. But the installation guide indicates that "all antenna feeders shall be installed in such a way that a minimum of RF energy is radiated inside the aircraft." I don't have a PhD in electronics so...