Those are horrors to build. Everything is snipeable in ATCS. Everything.
The best base I can think of is one in the middle base - If you place it right, only your base defenses are snipeable. However, this leaves it very easy for aliens to rest up (They just jump upstairs) and too easy for a tyrant rush.
The original base for ATCS is a hell to defend because of the side corridor and long distance from armory to main entrance unless you start camping the long corridor - which is generally a bad idea.
The side hatch is snipeable from either side no matter where you build, but can be do-able I suppose. Never actually tried though.
If you move to the anteroom in your main original base, this can work for awhile, but is again, sniper bait, and aliens can just use your old base or hte top of the middle base to regen.