In a glass glider, you can mount a
transponder internal antenna in the nose
cone, and trailer it to a power A&P who
can certify it for $90 or so.

Carbon requires either an external
antenna and ground plane (maybe upper
and lower) or routing coax to the fin while
making very sure it won't in any way
interfere with the elevator pushrod.

Maintaining power is a big problem as
you can't just slap a solar panel on a
turtledeck without treating the underlying
area to maintain structural integrity with
the higher temperatures.

Many gliders now run Flarm which does a
really good job of spotting ADS-B traffic
from way far away without eating up
power. Flarm gives pilots the information
to get out of the way of any ADS-B emitter
and should be acceptable as a minimal
means of compliance.

If the authorities allow us to use Flarm as
a position source to a Trig, we would be
visible to ATC and ADS-B receivers.