I to have a 2006 PW Plateau TS on the Dodge Sprinter chassis. I get 20-24 MPG at 65-70 MPH. However, I drop to 15 mpg when towing my 12 foot enclosed trailer with the Harley inside.
My only complaint with the PW conversion is there is little to no insulation in the walls or doors. Makes for really cold nights unless the heater is blasting. I did add a second coach battery, under the passenger seat, to allow the heater to run thru the night.
Bob