Like Deb & Ed said, a ditch is safer than an RV. If you are caught is open ground find the lowest point you can and lie down with your head covered.
The Red Cross has a good smart phone app that will send tornado and severe weather warnings to your phone. Search app store for "Tornado"
The odds of being caught by a tornado are pretty slim, but being prepared is the best defense. I've lived in tornado country for 45 years and have never even seen one. Spent a few nights in basements though.