I am a gas detection system engineer ontop of my swimming pool systems and I would never advocate the storage of LPG or any other gas cylinders indoors.
LPG is heavier than air although at certain temperatures it can float up, but we should regard it as heavier than aair which means that it will sink like water to the lowest levels and sit there until removed by air movement or other means.
There are many instances with the portable gas heater where they leak and the gas settles between floors and is ignited with a light switch etc.
Also be aware of under house storage for the same reasons.
Ensure all connections are tight and check for leaks with soapy water.
Check the connections to appliances at least once a year and test for leaks also.
Need any advice please feel free to email me.