Please, budding engineers, gaze upon this FOB and take notes:
It is compartmentalized.
It uses plasteel only where necessary to ease movement.
Cades are not flush with corners preventing xenos from hacking them apart in cover.
Ingress-Egress points in different compartments try to line up with each other so it's faster to move through them.
There is room for the tank to move in and out of the FOB.
It is not a perfect FOB, but it is a good FOB.
This is better than having 1 fob compartment with 3 layers of cades. Please learn from this example of FOB building.