On the 3way you can use a/c or propane to get it cold. Once you get it cold and are heading out for a trip it will keep it cold on 12v from the tow vehicle only, not from camper battery. It is 12v wired to aux wire on 7-way plug (center prong).
2007 Toyota Tundra Crewmax LTD 4x4 5.7l w/4.3r 381 hp and 401 lb-ft of torque
2012 Jayco 32BHDS
Me, Wife and 3 kiddos