There was a MG bunker on the inside facing the gate at Lahr, duty for that was interspersed amongst the lodger units. I agree that intelligence and police work are your first line of defense. However if that were to fail, it would be remarkably easy to penetrate a base right now. I would say the navy bases have the advantage over Air and army bases as duty ship crews have fairly quick access to small arms and ammunition.
Building some MG bunkers is easy, hardening your perimeter is harder, but doable in stages. Along the fence line, dig a ditch line and ensure vegetation is kept clear on both sides. Gates meant for occasional access, but can be accessed by public road on the outside need to be hardened with vehicle barriers. Main gates need to be hardened with concrete designed to channel and limit vehicle movement. Deployable vehicle barriers should be installed and guardhouses as they are renovated made to withstand small arms fire.
You are right the people part is the hardest part. You can have the commissionaires do the ID checking, but you should have armed guards to protect the gate and observe what is happening. You need a fulltime security office that monitors gates, fencelines and sensitive areas using PTZ cameras. You need to update your ID systems to allow for swipe cards, modern security systems will allow you to add or remove various access privileges. Checking manifests against cargo at the gate might be time consuming, but important. You can man the MG bunker if you get a viable threat warning to bolster the protection level.
The more you secure the bases, the less likley they will be targets. As for making bases look like a real military base and not a country club, I think the majority will understand pretty quick. The main complaint will be the slowdown getting in and out of the bases.