I tow with a 2004 expedition. It gets 12.5 mpg with nothing behind it and a tailwind. I'm not looking at what I get with a boat behind it. I haven't checked but I would be willing to bet that when I tow with my RV (a '92 safari diesel pusher) the RV gets better mileage than the ford.

Always borrow money from a pessimist. He won't expect it back.