Hi Colin
I've got the old style Sedona. It's a great bus to tow with as it's so heavy!
However - it can be incredibly thirsty if you keep your foot on the gas too much. However, if you get up to speed and back your foot off so you're just maintaining speed (throttle virtually closed), you'll be surprised as to the mpg you can achieve.
My last run up to the lakes (a five hour run for me) resulted in me getting similiar mpg WITH the van on the back as we do WITHOUT the van on the back! Hoorah!
Like I said - you do have to monitor your right foot! On a much shorter run (driving into a headwind), I had to use the throttle much more and my mpg suffered big style!
A tip I picked up on here too is to open your sun-roof (on the 'tilt' selection) to act as a mini-wind-deflector.
It works!
Enjoy your new bus.
Mac