Also, using a LP hose to inflate a sealed SMB runs the risk of over-inflation and bursting the balloon There should be an opv valve, but sometimes their isn't or it can't cope.
But if you have a BIG SMB and really like the idea of using a LP hose to fill it, consider having a dedicated LP hose, and remove the clip mechanism on the end so the LP hose doesn't stay attached to the SMB and drag you up during deployment.
If it doesn't have an OPV then it should only be inflated at the surface.......