An RV Fridge can draw around 3 amps AC or 30 DC when running. that's a lot of current. A GC-2 pair only has about 220 amp hours total 110 that you can use so that's 3 hours (less actually) per pair.
A Residential fridge is often a bit more efficient. figure 4-5 hours max and the Inverter may not let you run it down that far.
Also if the Fridge compressor is RUNNING when shore power is lost (Residential type) that ... May not be good depending on just how fast the inverter's transfer switch flips.. YOu can weld the switch.