Pirates! (I hate those filthy bandits.)

Perhaps one way to improve this scenario would be to add a buildable defensive turret with a limited (maybe 90 degree) firing arc? You could use it to cover the airlock when facing intruders, and if you're boarding an opponent who has one, you can use tactics like blowing a hole in the enemy hull and coming in from another direction.

Another option would be buildable chest-high walls, which could absorb half the damage of shots passing over them, unless they were fired from a spot directly adjacent to the wall.