I don't think it's that complicated, really. did you see the short live footage of the OK tornado? the two guys who shot it piled themselves into a mechanics pit that had been dug in the floor of their garage. the pit had a couple of metal doors that closed over the top and could be fastened down. the essential thing is to get below ground level and have an overhead secure door/ceiling. even if an F-150 lands on top ... you are alive. rescuers will be there within 30 minutes afterwards. they can drag off the debris. you and your family just need to be in 1 piece. that's all.

Pete2