If a computer on the RV is determining the mileage, it may or may not include fuel used by the genset. The " miles to empty" indicator will be using the actual amount of fuel in the tank and won't care what is using it. If you are calculating the mileage yourself or with an app of some sort, fuel used by the genset or engine is all the same. A drop from 7 to 4.5 MPG seems excessive though. If you get 7 MPG and travel at 70 MPH you use 10 GPH. if the genset uses 1 GPH you are using 11 GPH total, I think the mileage would drop to 6.3 MPG or a 10 % decrease to match the 10% increase in gallons used. Could have the math wrong as I did it myself. You experienced over a 30% decrease in mileage. Maybe there is something wrong with the genset to cause it to use so much fuel.
