There are videos on Youtube and photos on various survival forums like whenshtf.com where people have used containers or concrete pipe for underground shelter.
My next house will have some sort of underground room, not sure about the specs yet.
I did see a buried 20' container live and in person in Indiana. The guy dug a hole deep and wide enough to put 3-4' of riprap on the bottom and sides of the container. He plumbed in a sump pump to pump out the water. He built a "roof" over the container and poured concrete on it. Then he put 12" of top soil with sod on the "roof" which made the whole thing look like part of his yard. Inside the container was fixed up to be his reloading room and storm shelter with some supplies. The entrance was like any other storm shelter with a angled door and stairs going down. He wasn't thinking about opsec, just looking for space where he didn't have any. The inside was finished like a house...lights, heat, AC, very nice.