Regardless of the type of in-ground shelter you get, the fact is that it may be covered with debris after a tornado. 101 people were "rescued" the first evening after the tornado. Most of those were literally dug out from some type of in ground shelter. It doesn't matter what type of shelter, what type of door, what type of come-along/winch you have, if a house, car, tree, business or any combination of the above lands on top of your shelter you might be there for a while. Be prepared, have what you need in the shelter to live a day or two. Register the shelter with the city and understand that help will get there as quickly as possible. A signalling device (strobe lights, air horns, etc) might be handy items to include as you can hold those up to the vents, or any slight opening you can achieve with your shelter and greatly assist in identifying where you are and that you need assistance.