I actually have to agree that the risk of asphyxiation is real. I also maintain that if the tank is unrestrained, the risk of being whacked on the back of the head with it is higher.
I have spent a lot of time on fuels safety. Without a controlled mixing of fuel and air, it is REALLY hard to ignite propane, methane or any of the other -ane's in a ventilated space. If allowed to pool in an enclosed space, the barrier layer easily meets the mixture requirements just like the vapors from gasoline.
So use caution but also use common sense,