I located an old Forest Service comm center truck box that had been removed from the truck. It has double steel walls, insulated, with 7 windows and 2 doors with heavy deadbolts built in. The aft four feet feature an isolated room with heavy shelving and double-doors and locks. Overall, it is 12x8 feet (8x8 for the main room) and 7 feet floor to ceiling. I paid less for this than I would for the wood to build a simple box. The "extra" room houses my deep-cycle batteries and solar controlling system.