-34 degrees is a different story altogether. Propane has almost no vapor pressure at that temperature, so it requires not just keeping the fresh water lines warm, but keeping the propane warm enough to keep flowing. In those temperatures, pretty much nothing will do the job next to having some type of propane furnace or other heater and a way to circulate air between the bottom of the rig and the water pipe.
Propane boils/vaporizes at -44F
while not a lot pressure, you are not looking for pressure after all regulators are set in WC inches that equal to about 7 lbs