Check out Survival Capsule and decide if you want to go "solo" or make it a family affair. The big question is do you allow room for the mother-in-law? Then I noted that you have an option to select a color, that makes it easier to sell to the neighborhood committee regulating exterior home improvements. In my neighborhood we'd have to put a shake roof over the top of it!
In actuality the idea isn't too far fetched. If I lived in Ocean Shores or Long Beach here in Washington State this might be a good option since you won't be able to outrun a tsunami.
