Found these tips on the web to stop your LPG tanks icing up. See points 4,5 and 7. Unbelievable.

Prevent Propane tank freezing up
This is a very common problem, especially when firing quickly, using a 5 gallon tank, in cold weather. There are a few solutions you can try.
1) Use two or three tanks and switch between them in between each firing.
2) Connect two or three tanks together so the draw on each one is reduced
3) Use a larger tank
4) Place the tank in a tub of water
5) Drape an electric blanket over the tank
6) Fire slower
7) Rock or shake the tank - this is especially a good if you just need to fire a few more minutes to finish a firing.



Linkback: http://www.plumbers.co.nz/forum/gas-station/11/how-to-stop-your-lpg-tanks-icing-up-only-in-america/411/