Hauled millions of gallons of propane, butane, isobutane and stuff called alky feed which was natural gasoline and water with green slime in it. None ever froze on us. I've had propane in NM, OK and Va, all of which had temps well below 19 degrees. We had lines on propane vehicles freeze but it was from using pure liquid and not having the water heated in the radiator enough to stop the frost buildup in the regulator.It also pays to ahve them full incase the heat goes off in the house and you want a place to sleep.