Hi Shon,
Propane is a liquid when in a container. Propane becomes solid at -40. Propane GAS that we use for the forge is the determined by the amount of surface area that can give off the gas. If we draw too much gas off the surface of the liquid the temperature drops in the container (Bottle). If you are using a 20-30 lbs bottle, put the bottle into a container of water (like a small garbage can or metal pail/tub. The water acts like a heat sink and the bottle takes a lot longer before it is a problem and freezes up). Propane tanks for a residence or a vehicle are mounted on their sides, to create most surface area. This also means they have a different valve, so they only draw the Gas and not the LIQUID. If you accidentally draw the liquid, the flame will go through the roof. Soon no shop!!
I use 2- 100lbs tanks hooked together in parallel, this makes the surface area double and the draw from the surface half of what it was with one tank. Drywall people will sometimes hook 4 to 6 100lbs tanks together to try to heat up a place they are working, without the tanks freezing. You can get the proper PROPANE fittings from your local hose/fitting supplier.
Keep on freezing, that means you are working. Sometimes when the bottle freezes it is a sign to take a break anyway!!! :) :)
Neil
Neil