Just buy a bit bigger one, and fill the unused space with water. Every open now exchanges less air and you can turn it off for hours or a day without any impact of the temperature inside - water is good capacitor of temperature.
We fill it up with food that otherwise doesn't need to be refrigerated but they keep better at low temperatures, like fruit jams, unopened cans or olive oil. One could fill it with kimchi, beer or bottled water though.
