When we built our house, I had them excavate under our front porch and our garage and they both are full concrete except for the doors. I did not have a safe door installed, just insulated steel doors. I use the room under the porch(8'x8') for my gun room. It has a digital lock on the door and I keep my safe inside the room. No HVAC, but I do run a dehumidifier in the room and golden rods in the safe. The room under the garage is 30'x30' and gets used for storage or storm shelter if needed.