[Aleph]

You could counter with the big, punchy weapons that could strip the structure away quickly (depending on the point values you are playing at). Once that is gone, so is the advantage of that tactic.

You could also try to get in close and outside of the single firing arc he has armed, staying behind or in front of him, and hitting his weaker front or rear.

If you are inclined to collisions, while you'd only do armor/structure damage on his tough side for the initial impact, if you keep pushing, the next collision will cause damage to his side that hits the wall, where he has sacrificed defense. But you'd have to be willing to take it twice yourself for this tactic.

Or if you can withstand being in his firing arc for a bit, you can force him into collisions with the walls or other obstacles by boxing him in and not giving him the space to maneuver.