I used the Uavonics EXT version with internal electronic plastic dipole antenna purchased from Spruce. This eliminates the need for a ground plane. No antennas outside the airframe. Echo and FX are mounted on a small aluminum shelf I made and Velcro’d to passenger side wall, baggage area, above cut line, just under the main wing. The antenna is mounted vertically low on the rear bulkhead. RG400 cable between Echo/FX is about 10”L.
Hope this helps. Install is very simple. I posted pictures a month or so ago