Add static M2's, m249's and (especially at rearward bases) some kind of non-guided anti-air defense (dual 50's on a swivel mount that can't aim all the way down? Static minigun with unlimited ammo overheat bar?). Maybe even a static 20mm turret.
All of which can be disabled by RPGs/C4/tank and repaired by engineers.
For the primary purpose of giving defenders a firepower advantage and to make heli-drops more precarious.
Military style bases (usually the closest to spawns) could be far more equipped than central/city bases, it doesn't have to be even-steven for everything.