There has been a lot of good info here but as someone who was in a campground hit by a tornado there are circumstances that catch you by surprise. You think you are prepared but find yourself riding out a tornado in a hybrid travel trailer.
We arrived on a Sunday, the office was closed and our site info was left in a mailbox. Weather was not perfect but it wasn't raining or threatening. The campground was unusually quiet. We started setting up and the wind picked up. We leveled, set the jacks and got the canvas ends set up when the sky fell. We didn't have a chance to even think about a bad storm. Fortunately the huge trees that came down were in the front of the campground and the trailers hit were unoccupied. It happened so fast and over so fast we barely had time to be afraid yet be prepared.