I traded my in-line 5-cylinder Winnebago View for my new PC 2910D.
Below is the performance graph for the unit I traded in.
The specification for that motor-home is 17 to 19 mpg. Over 80+ thousand miles my fuel consumption averaged 18 mpg... highways, byways, AC, no AC, mountains, plains, good fuel, bad.
When the EPA emission requirements for 2008 came on stream it was necessary for Mercedes to go to a V6-cylinder engine to get the horse power rating back up to the HP of the previous in-line 5 cylinder engine. The upside was a larger chassis for greater Cargo Carrying Capacity and higher torque. Downside was 2 to 3 seconds slower 0-60 and 2 to 2.5 lower mpg. Fuel consumption is 14.5 to 17 mpg.
When the current emission standards came into effect in 2010, the power losses of over 30 HP were again a problem. To get back to the 5-cylinder performance, Mercedes introduced the V6 Blue Tec engine. It uses liquid urea (DEF) for the two catalytic nitrogen oxides converters, plus high fuel rail pressure and pattern-programmable multi-jet injectors. Upside is 0-60 speed is back up and mpg is improved slightly. Downside is a 6 gallon DEF tank that reduced storage and was problematic to fill. A new option for a small DEF tank located in behind the right headlight solves the filling issue. Fuel consumption is 15 to 17.5 mpg.
From these data and the performance graph you should be able to judge what to expect with a Sprinter-based class C motor-home.