Question on fuel consumed by our generator AND ??

My generator, running our house type refrigerator and both AC units, uses about 1 gallon per hour. And about .3 gallons per hour just running the refrigerator. While driving our gas mileage drops from 7 MPG with no generator to 4.5 with the generator. This winter I am getting an inverter installed so we can run the refrigerator with the inverter instead of the generator. At $3.50 a gallon for gas, it will not take me long to recoup the expenditure.