I had a workshop studio that was made of a half-size shipping container (in the business apparently they're called, "conex boxes"). The conex box can also come in 10', 20' or 40' lengths. Just for "fun" I thought I'd compete with the Japanese micro-apartments and use the mid-s...
Basically, a shipping container is pretty good for above-ground fortification as long as you fix any chemical problem. You can decide to bury one (or more) but to do it properly (not even counting the tactics and other considerations), you’ll have to spend a lot more money to make it...