Just returned from a slightly different trip in our 2012 Nexus 24' C {E-350, V-10}. This trip we left the bike and trailer home and unloaded a bunch of stuff we would not need as we were going to staying with friends in their driveways.
We were running about as light as ever, probably well under 11K# so I adjusted the tire pressures accordingly {60 on the front and 65 on the rears} and set the cruise control at 65. Mostly interstate between Tucson and San Diego and we got a solid 10.0 mpg.
Fully loaded we normally average 9.5 with a little generator time thrown in but cruise at 60 - 63.
Towing the 2,220# bike trailer combo knocks us back to 8.5 - 9 again cruising 60-63.
:C