I believe your refrigerator was originally equipped with a 250 watt heating element. Now the replacement element for a RM760 is rated at 295 watts.
Dometic Heating Element 295W 3108702386 | eBay
The 12 v side uses about 1 amp an hour.
A 900 watt generator should be able to run the refrigerator, but if you turn on a TV or a few incandescent light bulbs you'll exceed your capacity.