Vikings are pure gliders, I have no idea how much they ever get out of the circuit in Air Cadet flying. The commonest device for lookout assistance in gliders is FLARM which comes in at under £600 for the most basic version - the difference with more sophisticated models is not in the FLARM itself but if it's an IGC logger or not as well.
In the many club & private gliders that have it fitted it is often simply stuck on top of the instrument cover with something like very heavy duty Velcro. It needs a 12v power supply, it's very tolerant of low voltage, the big gotcha to be careful of is that the way the power is supplied won't interfere with ejecting the canopy. In some gliders the area it's normally mounted leaves with the canopy, in others it stays with the glider.