We keep a layer of water bottles on the bottom of our freezer compartment. Takes up a couple of inches of space, but keeps the freezer freezing and the bottom cold even when traveling. Use them for cooling bags of drinks and etc. when out and about as well. Works for us and doesn't cost anything extra.
2010 Montana 3665RE, wet bolts, etc.
2006 Ford F350 Diesel Dually, air bags, Softopper, Aeroshild, etc.