Assuming that there is no moisture in the propane causing the regulator to freeze up, I will add to the recommendation for replacing the regulator. I have camped in sub-freezing temperatures and all the normal propane appliances (cooking, heating and hot water) continued to work. It is possible that if propane is consumed at a high rate, the liquid evaporating in the tank can cool down below ambient temperatures. At 30º F the vapor pressure in the tank is only 51 PSI and at 0º F the pressure goes down to 24 PSI. The typical RV has a two stage regulator with the first stage reducing tank pressure to about 10 or 15 PSI and the second stage delivers presure at 11" WC (about 1/2 PSI.) This regulator should be able to keep up with the BTU demand of all the propane appliances on the RV. I had a similar problem, but at the opposite end of the thermometer. The temperature was in the high 90s and the temp on the road was even higher. I estimate that the propane tank pressure was about 170 PSI. The hot water heater would run, stop and after relighting would run out of gas. The BBQ grill attached to a separate 10 PSI regulator ran fine. Turning off the main tank and bleeding off the pressure and tapping on the regulator with the handle of a screwdriver, the gas worked for about a day or two but stopped. Replacing the regulator solved the problem. Your milage may vary. In extreme cold conditions an tank heater would help. I heard from a co-worker that up north, some propane retailers add methyl alcohol to the mix as an antifreeze. Maybe someone can weigh in on that. One more thing to check is a surge check valve that maybe built into the system somewhere. Some connctors on portable tanks have those. The idea is that if there was a break in the line, the high flow rate would shut off the flow. The problem there is if the check valve is bad or the BTU demand exceeds the check valve, gas will cease to flow. Then you have to shut off the pressure, purge the lines and then start over again by SLOWLY opening the tank to avoid a rapid flow through the check valve and you are back to where you started. I had a work truck that had high BTU heated ventilators for tents and underground vaults. The safety people ordered the wrong equipment that when the temperature dropped, everything froze up. This is why I use gasoline or diesel generators in the winter. One time I actually put an electric blanket on the propane tank.
