Strong by walls and cellings but weak by doors. 8 doors with luck to reach tc, 10 without luck. If all base is in steel, it's like 8*4=32c4 or 10*4= 40 c4. 4 walls to reach tc. So 4*13= 52 c4. It's unbalanced. 4 walls stacks need at least 12 or 13 doors to reach tc. But the base is good. Just add 3 foundations around your 4 entrances. Then add 4 doors in spirale to reach the entrance. Here you have 12 doors before TC