well...heres are my wishes.
1：hitbox Armor Value
each face of hitbox will have a value called "Armor Value"
Like the following picture
We can set a value in each face
And in the other hand,shell will also have a Value called"Piercing Value"
then,here is the point.
if a shell hit the hitbox like following picture
The Piercing Value of Ammo is lower than the Armor Value in the face that been hit
then it won't cause any damage on the vehicle.
and,if the The Piercing Value of Ammo is higher than the Armor Value in the face that been hit,the it will cause damage on the vehicle.
we can add a new hitbox called "player"
if that hitbox is destoryed it will also killed the driver on the vehicle instead to distory whole vehicle to kill the driver
Just some idea