IMO, HVAP ammo should be a vet 0 ability for USF AT guns and also Jacksons. That would go a long way to making them better at countering heavy armour - but still at a cost. Particularly in the long haul when attrition starts taking its toll and you have fresh units to replace some losses.
You can take for him another crew (like 3vet rear echelons) and you gonna got 1vet Slugger. Tadda!