you’re also talking fully tactical. They’re looking at fixed bases to begin with - which also have their purpose.
They also aren’t talking about civy 5*8 hour days to get 40 hours, but rather a start one morning, and ready to move in the night after that.
Double walls with fill in between would be really tough.
I like it. Tough and durable. And one can set the fill percentage to vary the toughness. They must be using a fast setting concrete, so it won't collapse between layers. I have printed various things on my 3D printer, and have found that it doesn't take much of a fill percentage (cross-hatching in between outer walls) to strengthen an object, usually between 5 to 10 percent, and make it very sturdy.