If I follow what Jeannette is recommending, use a back-up power supply in conjunction with your generator to stabilize the power. Back-up systems like those provided by Xantrex come with an internal power inverter to turn the DC battery voltage into AC power. Get one with a big enough inverter and a big enough battery.

I have the XPower Powerpack 400 and I doubt that it has the reserve power to ensure stable power for a refrigerator. For this application, I'd go bigger.