If the tanks are properly installed then only gas enters the hose, to get it to become liquid you either need a whole lot of pressure, or a whole lot of cold or both.
IF you are worried, Move the regulator as well as the tanks, Regulator output is (Somewhat rounded) 1/2 PSI, not nearly enough to make propane turn liquid at temps much above -40 (Your choice of thermometers) Of course, at -40.. Does not matter how long, or how little pressure, it's liquid.
Second. if you run a good size 'U' trap. if any liquid makes it's way into the hose the hose will frost very quickly,,The regulator takes a couple minutes more to freeze up.