I never have used one.
I do however take a big super hot class/cup of water out to the tank & proceed to make a narrow stream down one side. The gas will absorb the heat and make the side of the tank stay cold. Where there is no gas there is nothing to absorb the heat so that part of the tank stays hot.
Diane & Jeffrey Wilson
Dennis (the Jackshyt ) part Jack Russell part Shytzu
Ricky aka The rotund one
Sherman ( the Pomeranian ) he runs the show!!!
2006 Jayco Eagle 322 FKS
2011 Toyota Tundra Crewmax. aka The RED Tundra !!!!