Some ideas, some maybe good, others may not.
1. GV's. This is probably the more contentious issue to be brought up but here goes.
A. Concrete hero's, when an enemy is present within 2k of a base there ought to be a specific location in which GV's can successfully land. I am not talking about generic concrete but a unique location similar to a rearm pad for AC. This ought to mitigate the Tiger 2's powering on concrete when you either range them in, or land a nice shot.
B. Resupplying. GVS ought to be limited to one major repair per sortie. I have literally turreted the same wirb 5 times in on sortie.
C. Modeling damage for troops and supplies for in bound GV's. You would think that a raking burst of 50 cals would turn any living creature in the back of an M3 into mush, this may also let the German Half track see more use.
D. Anti tank ditches. It would seem logical that a significant front line military installation would have anti tank trenches in the vicinity to funnel potential attackers into a specific location.