No experience with gasoline engines...but it should be very similar to diesel gen sets..rule of thumb is a pint or a pound of fuel per hour per kilowatt. So do an estimate of your average electrical load for one hour, say it's 3,500 watts, or 3.5 pints of fuel. I used that in years past to calculate fuel needs on unmanned refrigeration barges going to and from Alaska. Modern engines with supposedly environmental friendly efficiency seldom do much better in spite of the advertising hype.
