Ideally, a V base should have 4 manned positions around the core of the base that can not be killed when not manned, or ideally, from the air. They would have to be shot from the ground while occupied.
Not to make it harder to land grab V bases. If you want to do that, defend them.
But to give defenders a fighting chance if attacked by ground vehicles.
Should be at least 2 88mm or equivalent guns, and a pair of 37-40mm guns.
Those along with the 2 auto acks we currently have should do the job.