Exactly. We can maintain quality of life running the generator 4 to 8 hours a day (or less) in a catastrophic situation All we really need for survival is water so we could just run the generator to refill our 2,000 gallon water storage tank from the well.400 gal x .7 gal/hr = 280 hrs of run time
280 hrs ÷ 24hrs/day = 12 days of fuel.
I'm missing the 3 months completely isolated part. Are you going to ration the run time to stretch it to 90 days?
We have plenty of long life food available that isn't refrigerated if we lost the fridges and freezer. Another factor is I haven't calibrated the fuel tank gauge so the 0.7 gph fuel burn is a tentative number. Oh, our stove, clothes dryer, water heater and emergency heat is propane, we have a 500 gallon LP tank and burn about 150 gallons a year.
So I think I have most bases well covered for 90 days or longer.