There's a calculator here: https://www.batterystuff.com/kb/tool...-inverter.html
You would have to know the AC amp draw for the refrigerator AND the DC and draw for the inverter to get an accurate estimate, but I would guess you would be running your generator. A LOT so you don't fall below 50% on your batteries.
Another thought, if you have the space in your inside propane fridge, would be to use your outside fridge as a cooler. Have two sets of blue ice bricks, one for the outside fridge to keep drinks cold and one in the inside fridge refreezing.