7-9 mpg is about average and is dependent on many factors. Maintaining 55mph for long distances, on flat terrain, without stops and starts, no wind and tires inflated to reduce rolling resistance, will occasionally get you 9-10 mpg. A class C has a lot of weight, rolling resistance and flat front and rear. Not aerodynamic in any sense and mpg is not comparable to cars/SUV's.
Ads say my Subaru Forester can get 32mpg (ideal conditions) I get 23 around town and 28 on highway in SoCal terrain.
Best to relax and enjoy the trip, use the transmission properly on grades, and keep speeds constant and 55mph when practicable. Your mileage may improve with break-in. I take some people's claims of 10+ mpg with a grain of salt. It's easy to miscalculate mpg.