Travel trailer "vs" fith wheel --MPG to tow

This is similar to an episode of Mythbusters years ago where they tested the theory of a trucks tailgate being down increased mileage. The myth was busted as the truck with the tailgate up had much better mpg.

I can't find the video on the net but I remember them doing test in wind tunnels and it clearly showed the difference.

Somewhat off topic but still interesting.