I can see this topic is quite large!
Alright, to answer your questions, I thought of turrets, but they could need a LOT of work. Would they fire if a teammate was in the way? Would they sense walls that are shoot-through or not?
The base would be a colored mesh (Like i have a clue of what that is), that causes enemy bullets hitting it to explode, but deal damage. a Counter would appear on the base to show hp. Maybe you could see on radar if it was strong (100-70), damaged (69-30) or critical (29-1, since whats the point of zero?). Upon destruction, a shockwave of large size (100 units? 500? 100000?

). The base is then gone forever. When a team wins, the game "resets", as the objects reappear and everyone dies.
Back on turrets: These could be types
Gun turret: Fires a spray off bullets near enemies.
GM turret: Fires GMs at enemies within locking range. STs are not noticed.
Laser turret: Fires lasers at enemies. CLs are simply ignored.
Smart turrets: They are the upgrades of any other turrets. They don't shoot at enemies behind walls, and don't fire when a teammate is in front.
Dumb turrets: Downgrade to any other turret. They are more prone to waste shots at enemies well out of range.
Turrets have a settable number of hp ranging from 10-50
(My hands are getting kind of clumsy here....)
Bases could have mounted turrets protecting it. Now, this might sound stupid, but what if you could pick up turret containers and drop them off the deploy? They would need shot limits, otherwise they could spawn kill.
Own team shots don't hurt bases.
Now imagine this: A base is surrounded by walls that go up indefinitely, but they can be destroyed. They'd have 30 hit points, and when they fall a small area is buried and destroyed, or dealt 10 damage (Including other wall sections. Anyone want to play dominoes?

). They could have mounted turrets. Destroying the wall kills the turrets. Once the walls are down, you must destroy the base. Lather, Rinse, Repeat several more times. Oh, and defend your base, too!
The Pen is Mightier Than the Sword.
Okay, you get a Bic, the orc gets a long sword.
He cuts the Bic in half.
Then he cuts you in half.
Oops, I meant quarters.