I didn't have a 320 (had 327) in my installation but somehow I "blew up" the transmitter on my GTX327. Long story, but changed the installation of the GDL82 to the avionics bay from under the seat and now a very short RG400 to the GTX327 . I called Garmin before making this change ( talked with two different Techs )and they said "no problem". On my next transponder/IFR check it FAILED. Transmitter was now 48 watts and off by 4Mhz. Not one ATC facility ever said a word.
Why did Garmin specify the GDL82 be mounted under the seat in the bottom of the airplane? Hmmm.....