Gliders have been using a GPS based system called FLARM for a number of years.
More common in Europe than the UK (was developed for use in the Alps) but the take-up amongst UK pilots is increasing and I can thoroughly endorse and recommend it being small and self contained and would be an easy fit to the coaming of the Tutor. Only disadvantage is that it only warns you of other Flarm equipped targets but as a supplement to the Mk 1 eyeball it does what it says on the tin and in the event of an alarm, it gets you looking in the right bit of sky for what it considers to be the highest threat.