Bunkers are static defenses, not a place for CR5s to hang out and make command calls. Some have tunnels that link them to the other bunker about twenty meters away... worthless.
Bunkers are designed to be a defensive strongpoint. DEFENSIVE. Simply sitting there all pretty-like is not defensive, it's rather offensive in that my senses of strategy and tactics and working knowledge of defensive perimeters are offended.
A bunker should have a built-in weapons system. Pillboxes in Hawai'i featured shore batteries in case of enemy ships, and they had anti-air flak cannons, machine guns, and mortars. Modern-day bunkers are equipped with a zig-zagging double-back entrance system so tossing a grenade inside isn't that easy, and they have a WEAPONS SYSTEM (hint, Sporkfire, I see you coming here). For more details, on a kick-ass idea that has 3d graphics and is highly well-thought-out, see
ZOMBIESIDE
Something along the lines of a cannon upwards of 20mm (no rotary-12, that thing sucks), a modified Phalanx turret (remove the armor and "cockpit", just put the gun there), or a completely new machine gun specifically designed for bunkers and only bunkers. You can even sling a grenade launcher underneath, so you've got a machine gun and an area-effect weapon.
And yes, TheN00B, you're supposed to be able to clean a bunker with something like a grenade, Thumper or a Decimator, if not a Marauder mortar or 75mm cannon. That's what they do, and that's why the flamethrower was invented for 20th century combat.