Another possibility would be to keep the pork targets, but make the number of convoys that successfully reach the base effect the 'hardness' of the pork targets.
Say they have a default 100% hardness, and say a convoy usually arrives every 10 minutes. Say that convoy repairs the hardness of the pork targets by 10% every time it arrives safely.
Pork targets would likely need their base hardness upgraded to make this work, but the theory is, in order for someone to pork a base completely for more than 10 minutes, they would first need to bomb out the targets on the airfield, THEN go out and hit every single convoy that is dispatched to prevent even soft, but still usable, troops ammo and extra fuel from coming up on the base again.
In this way, a base can still be porked, but continued attention would be required to keep it that way.