One of my major concerns living in Georgia in a house built on a slab is finding protection in the event of a major storm. Our plan is to take refuge in the truck, inside the garage, hoping for some protection from debris and avoid being drawn into the vortex.

A storm shelter is not practical.

Look into a small Monolithic Dome storage building for your backyard. It doesn't take up much room is pretty darn strong. I have been researching these things (domes) for years. They are pretty strong and easy to put up what you need for purposes of storage/shelter. http://www.monolithic.com

Standard Disclaimer: I got nuthin' to do with these guys financially, familially, or anything else.