With the ballista tower, when on high ground, if you have maxed out undead skills it should have extremely big range, and enough for all your towers in night missions.
Try maxing out war chief, then using the bunker den for massive critical hits.
For more power, maxing out all of the orc skills for almost constant blows, and if you add frenzy each time the bunker defeats something, it somehow manages to shoot FASTER.
Geez. I play this, and there are annoying requests, but I close those. I leave the game because of a crash and IT RESTARTS THE GAME FROM THE ABSOLUTE START!!!!! However I like the game so...4 stars. Maybe 3.