The Normandy expansion introduces several new armored units, among them the Stug III G assault gun and Jagdpanzer tank hunter.
If you look a the miniature, you'll notice they have no turret and the gun in built with the hull/chassis of the vehicule, meaning it can only aim forward. Those vehicules were not meant to be tanks, but rather tracked antitank guns, and proved most effective on defense when camouflaged and waiting for the ennemy armor to show up, rather than on assault. On a side note, these german vehicules were manned by artillerymen, not armor troops.
However, judging by their game characteristics, both the StuG III G and Jagdpanzer are superior to the Panzer IV, while in reality, their lack or turret made them a poorer choice on the offense.
So in order to stick back with reality and represent the lack of agility of thoses turretless armors, I imagined this simple house rule : like Heavy Infrantry Weapons, turretless vehicule cannot be activated with a fire and movement action.
On the other hand, the american Gun Motor Carriage M10 Wolverine was also significantly less armored than the M4 Sherman, resulting in higher losses when wronlgy used as a tank. It suppose lowering its armor value from 4 to 3 would do History justice.
Lastly, this is no house-rule but a call to your intrepretation : the M10 has an Open Top, described as "This véhicule is vulnerable to suppressive attack".
Fine, but what does that mean ? Can squads use their anti-infantry firepower to deal suppressive dice to the M10, or do they still use their anti-vehicule firepower ? What about tanks then ? Or am I just completely wrong, and th only meaning of this trait is than the M10 can be only suppressed by mortar attacks ? I guess that's what makes the most sense, but your opinion is highly welcome ! :-)