I am using Garmin GPS MAP 60 CSX with an external active antenna (Model MK-76) connected which I usually place (with double-sided sticky tape) to one of the windows (inside). The antenna cable is long enough to place the GPS receiver at any convinient location in the cockpit.
If you only want to track the flightpath, the GPS tracker (Travel Recorder) from QSTARZ BT-Q 1000X works fine and gives you approx 20 hours of continuous operation.