There's quite a lot of silliness being talked here.
I think you'll find that cheaper fridge/freezers have only a single compressor and thermostat, so what happens to the freezer is governed by the fridge temperature. In low ambient temperatures, the fridge will switch off, long-term, and so the freezer will gradually come up to ambient temperature.
More expensive fridge/freezers have dual compressors with separate thermostats for fridge and freezer. They will always offer superior performance but still cannot cope with very low temperatures.
Why? Because modern refrigerants do not work properly at very low ambient temperatures. So forcing the compressor to keep working at low temperatures doesn't do a lot to help.
For the same reason, bypassing the thermostat on a single-thermostat fridge/freezer or forcing it 'on' will not work either.
That's why, if you take the trouble to check your operating instructions, you will almost certainly find they say an ambient temperature of at least 10°C is required. Many will demand 16°C minimum.
The only satisfactory solution is to increase the ambient temperature, which is why Trebor's surround is the best answer here, unless you can find a heater as described by Jacquelyn, but most of them are from the US and hence 110V. Of course, you may be able to bodge some sort of heater for the compressor - just don't overdo the heat!
Dave H
January 2010