Get a bottle of soapy water and star spraying all the connections. Its not really normal. it is though normal to develop leaks, of have leaks get worse with the cold weather.
Its fine to leave it down for a few days.
If you had a crack in a bag, it would hold air for a second, and you would know.
More than likely its a leak at a connection. From your description its always been there, it will continue to get worse. The good news is the worse it gets the easier it will be to find.