Planning a get away soon. Looking to purchase a used RV. Need to know what kind of mpg I can expect to get out of a 22-28 foot C-class(van) RV. Engine size will most likely be a 350-400ci. I'm seeing a lot of Ford E-chassis for sale so that might be my choice. Any one have real world mpg for this kind of RV? Also any thing I should know before purchasing a used one. What to look out for, etc.