Hi Ben,
My investigations suggest that even a small 12V 'efficient' fridge can easily use as much as a big (as tall as me) fridge/freezer. Our is rated at 0.75kWh/day though actually uses 1.1kWh/day, but that's still less than the 12V ones I've looked at. So I suggest that you consider an A/A+ mains fridge plus good inverter.
FWIW here's my review of ours: http://www.earth.org.uk/note-on-Siemens-KG34NA10GB-upright-fridge-freezer-REVIEW.html
Go and look at http://www.sust-it.net/ and the Energy Savings Trust appliance info.
Rgds
Damon