First, the bad news: there is no defense in a panzer against a properly-flown A/C equipped with HS cannons. Your driver may seep before you die, but die you will. (Note to HTC: the Mk 108 30mm should be less effective against Panzers than even the .50 cal)
Second, listen to what wmutt says, it's good advice. Personally, I don't put much faith in the panzer's mobility: I only move until the guy drops his bombs. Then you might as well park (for better accuracy), and open up with the coax at d1.5. When he gets closer, go for the "long ball" with AP and HE.
I have gotten kills with the Coax. Even at that caliber, a good long burst in the same place will eventually hit something critical (usually the engine or the wing root).
If he runs an attack above your ability to elevate your turret, you're dead.
(for further tips, see my "Tank Dweeb" post below)