As towing seems to be impossible, to me the perfect AT gun right now would have two "states" (maybe set by the up/down arrows):
- One "static" state in which you can aim and turn the gun (but not move it)
- One "movement" state in which the gun can be moved (maybe faster than now, depending on the gun's weight) but you can't shoot. Ideally, the barrel would be lowered, the carriage a bit risen, the stabilization arms regrouped in the axis of the gun and the guy manning the gun would be a standard soldier walking near the stabilization arms.
This way, the AT guns are restricted to a defense/ambush role as they should, can't be used while on the move (letting this feature to vehicles only), and can be set up easily all over the map.