I work with Propane and heaters, no heater is completely "safe" inside unless it is vented. So leave a little air movement at least, and be careful. The way it works to fill small tanks with a #20 cyl is by gravity to transfer the liquid,and if you have a newer cylindar or one that has been filled in the last 5 years they have what is called an OPD and it has a float in it so you cannot overfill it. This also prevents you from tipping it upside down and having anything come out of it, which youneed to do to transfer the liquidwhen you hook up a "hose" to fill a small can. We actually use old cyl valves to fill the small cans because they don't have floats. Sorry to give you the bad news about the propane. One idea is that you can purchase #5 or #10 pound cyl.(they sell them at a fleet farm or that type store) they have the same valves as a #20 lb cyl. so you could have a "sunflower" or that type of heater. and They are light enough to bring out on the ice if you have a bad back.