I'm planning to install an underground safe room in my new house that will be under construction within the next two weeks. At first we planned to build a 10x10 concrete room but this would be pretty expensive. I have recently been considering buying and burying a 10x20 shipping container. Either will be accessible by a small staircase inside the house so we don't have to go outside to get in the shelter during a storm. Have any of you ever installed either and what would you do different looking back. Pros and cons?