Antenna Install in a Metal Glider

Happy Easter everyone! We have a IS-28B2 Twin Lark which we use quite a bit for instruction, it is good for spinning and intro into flying complex gliders (flaps & retractable gear). It is due for a complete overhaul which will include a new radio with a repeater control unit in the back for the instructor.

Since we´ll then be re-working the whole radio install anyway I have been considering doing something about the dragmaster factory radio antenna that looks more like a car antenna installed ontop of the fuselage tail boom. For you experts out there what would be your recommendation for an interior radio antenna install (or a low drag exterior install) in an all metal glider like the Twin Lark?

Many thanks in advance,

Markus Graeber
Aeroclub de Colombia