Towed artillery is not a good idea imho.
All it would serve is to take an active player in the game and make him static. Thats less fun for him, and the guy wanting to fight him. How often do you see wirbls just sitting on there base, not really participating in anything, waiting...serving as a deterrent perhaps, but still not promoting gameplay (which is fighting each other)
I can see towed guns for only two things.
Being the easiest stationary target to kill if it's actually shooting at something.
Sitting there being useless and wasting everyone's time until someone spots it and easily destroys it.