Simple 10 x 10 turret setup to kill Small/Medium demolishers. Uses 20 Red Ammo per turret. I made a logistics request for turrets and ammo it's simple to load up on supplies when it's time to head out kill a demolisher.
For Big Demolishers, put down more turrets. 20 x 20 should work depending on your upgrades.
10 x 10 array ==> 100 turrets + 2,000 ammo
20 x 20 array ==> 400 turrets + 8,000 ammo