I live in a centrally heated house which can mean wooden instruments can dry out really quickly. Using this small humidifier which sits between the strings, allows me to keep the instruments, (when they are in a hard case), properly humidified. When the house humidity is low, 30%rh or lower, my instruments can sit at 50%rh (+\- 5%rh) maintained easily by adding de~ionised water to the sponge when needed, until the humidity reaches your desired level! This little ukulele humidifier easily fits between the strings of my 8 string tenor & 8 string baritone ukulele’s.
Obviously you also need a humidity meter in the instrument case to find out what the humidity is!