You'd definately have to create an individual "turret vehicle"....
A friend of mine once made a working crane which had this "turret control tower" on top of it, so that my kid back home could actually get in as "gunner" and use the turning function of the crane. And that crane house (or 'crane tower') was made out of a static M2MG, as far as I remember, which was simply setpossed upon the (static) crane base. ;D
I'm afraid it would take som'n like this to do it, matey! :-\
and then ya could make a custom tank (a real tank) that got replaced, as ktotte said, with the fake tank objects when it's been destroyed.
The new Mi2 russian choppers addon have this "wreck_replaces_vehicle" function (script).
:cheers: