How can I make a hidden storage bunker.

Just a NOTE Here: Conex Boxes can be buried, IF you supply internal Bracing Supports, between the SideWalls, every 4 feet, vertical, and 6 feet along the length, and have Floor to ceiling braces down the center, every 6 Feet, until the soil around the outside settles and gets compact. This usually takes about two years. There is a fellow up in Alaska that built a Living Space, out of 6 ea. 20 ft Conex Boxes. Two buried, two for the Main floor, and two for the Second Floor. He braced the buried ones for a couple of years, and didn't use them, and cut holes between the upper 4 for doors, passageways, and stairs, then fabricated and welded sealing lips between the two sides of the openings to seal up the openings, from the inside. In the Spring, when he does his Spring Cleaning, he just opens up the BIG Doors on the ends and sweeps out the clutter, and closes them back up. The buried ones are uninsulated, and the top 4 were Refer Boxes, and Insulated. He sold the Refer Units off the boxes for 60% of his costs, to a local shipping company for spare Parts, and built the entrance and windows in that end, for the main floor, and just built insulated walls with windows, to replace the Refer Units, in the second floor boxes. Once the soil had compacted and settled for two years, he cut a stairway hole down to the Basement Boxes, removed the supports, and built shelves and installed his shop and tool room. It worked for Him...