The lower hull is on a different sprue, which meant on another mould. We only have budget to make changes to a single one... the upper hull is more important to this respect.
Ah, then you won't be getting to the slight modification I was going to suggest which is on a different sprue. It's also not super important, but an idea you might keep in mind for other projects.
I'm building a StuG kit right now, and one mod I'm adding in is an extended tab on the barrels of both the long 75 and the Howitzer. That way, I don't have to glue them, and I can easily swap out barrels. The added length of the tab means that the barrel won't easily fall out of the mantlet. The tab molded onto the barrel could have been extended to reach all the back to the mantlet plate for a very secure hold even if not glued in place.