What I see here in the south where tornadoes are a regular event, concrete septic tanks are are modified at the point of manufacture, and sold as shelters.

These are poured with a vent opening in the roof and a doorway at one end. They fit the roof vent on and a steel door in the doorway. These cement companies sell them and deliver them to one's prepared location.

The new owner then piles dirt over the sides and tops of these shelters. The owner then equippes the interiors as they see fit.

The old rule concerning the "only bomb shelter in the neighborhood" applies everytime bad weather moves into an area. All the neighbors show up to get shelter from the storm. One friend of mine has set up benches along the walls to have room for everyone who shows up. This prevents doing much else to the inside since there is insufficient room to have shelves of supplies as well as accommodating all the visitors.

If they did try to store disaster supplies in the shelter, everyone of their neighbors would also have a complete inventory of those supplies stored in the shelter which would cause more problems.