I had the same issue the first time around. My solution was to spend some time building a massive wall (using cliffs to help provide a natural barrier) around t

I had the same issue the first time around. My solution was to spend some time building a massive wall (using cliffs to help provide a natural barrier) around the perimeter with a belt full of ammo that refilled all of the turrets. The defenses rarely engaged the enemy but when they did it helped that they destroyed a segment of the wall instead of my base. Made it far more enjoyable to fight the buggies.