If a tank is moving, or in the open, then its usually an easy target for aircraft. If the tanker whinges because planes can easily take him out - well I'm afraid that's close to what happened in RL. The Germans paid dearly for losing air superiority.
However, a GV close to (or under) trees that has also been stopped for a while could be camouflaged and be very difficult to spot.
I suggest therefore that a stopped vehicle can 'Camouflage' itself (press a button) and for a few seconds it can't fire or move. At the end of that period it's 'Camouflaged' and much more difficult to spot. As soon as the vehicle moves though, the 'Camouflage' is removed and it's visible from a distance again.
I reckon this could work great with digging in Stugs for ambush (when we get them) and hiding M3s and Jeeps (for spotting, maybe) and such.