My idea:
Lets focus on the "panzer" part of these grenadiers and give them vet1 ability that would somehow improve their performance when there is a vehicle nearby. What kind of ability? I'd go with something akin to sherman vet1.
Multikill with single stone.
-unit buffed
-encouraged use of light vehicles
-can't be blobbed as it'll net same results as now
Only disadvantage of the idea is, it wouldn't do them much when there is no owned vehicle around.
+1 on that.
I think the "Hirt the Dirt" ability is perfect for that.