Use a hard case and a bass stand.
I find storing a bass in a hard case (as opposed to no case or a soft case) keeps it better in tune. This protects the bass from temperature/humidity and the protects the tuning pegs from accidentally knocked around. Jamming a bass in a tight fitting gig bag could also cause the tuning pegs to move.
Leaning a bass against something (as opposed to using a bass stand) on its headstock could also move the tuning pegs.
I find storing a bass in a hard case (as opposed to no case or a soft case) keeps it better in tune. This protects the bass from temperature/humidity and the protects the tuning pegs from accidentally knocked around. Jamming a bass in a tight fitting gig bag could also cause the tuning pegs to move.
Leaning a bass against something (as opposed to using a bass stand) on its headstock could also move the tuning pegs.
