I think I might have figured it out, take a look at the two images, as you see in the second image, the tank is colapsing in on istelf.
I went into the Physics Asset for the tank, selected the bones/joints in the top left of the below screen shot, and then selected the constraints in the bottom left. I then selected “Locked” for these as you can see on the right side:
After that, I started my game and they no longer collapse.