The Corrupted Battle Tank features 2 destroyer barrels, 2 overseer barrels, 2 necromancer barrels, and 6 gunner barrels. The Destroyer barrels' bullets go much farther than the gunner's but fire less often.
Using a quick tank like the fighter will really work. It is nearly impossible to kill alone, so you will need most of your team helping. Stay at a fair range, move out of the drone's way, and avoid the destroyer barrels.