NAV radio antenna can go on top of the tail also, the rabbit ears type are quite common.
Markers go underneath, if you want one, and a storm scope if you desire.
Transponder typically under the plane beneath the seats. If you have two VHF coms you might have one above the tail cone and one under the baggage area floor.
GPS for a GTN/IFD is best on the top of the tail cone, but I see some under the roof. I avoid putting them in the engine bay.
The Dynon GPS antenna is best mounted up front, do not run the SV-GPS cables beside any VHF comms for any distance.
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