When tracking V10 MH gas mileage, be sure to know how the automatic shufoff mechanisms on gas pumps interact with your particular MH's gas tank filling tube and evaporative system.
We had our V10 motorhome for a couple of years before realizing that the motorhome's tank would always take somewhere between 5 and 6 gallons more after the gas pumps would automatically shut off ... so accurately making gas mileage calculations was somewhat swamped out by this variability in how full the tank was winding up.
We now force the tank to take an additional 6 gallons after gas pumps have automatically stopped. This helps make accurate and consistent gas mileage calculations. It also helps lengthen travel distances between gas stops.