Here is an article I just read about mortality rates of tornadoes when you are in mobil homes:
http://www.usatoday.com/weather/stor...-cleanup_N.htm

Part of what it says is that: During tornadoes, the fatality rate for people who live in mobile or manufactured homes is 10 times higher than for those who don't, ... such structures "are prone to catastrophic failure at a lower wind speed."