This is something new I just designed and I call it the Fish’s Uke Cookie Humidifier. Fish for my last name.
It is very important to use a humidifier in your ukulele or guitar especially in hot dry weather to keep the wood from drying out that can cause the wood crack or split. Rubber tube humidifiers alone work well when stored in a case but not when setting out because their wick dries out too fast with the open hole in the instrument.
Fish’s Uke Cookie Humidifier covers the open hole with a hole for the humidifier. The hard wood cover has a thin soft foam back to keep from scratching your Uke top. To use it slide the wood disc behind the strings and drop in the humidifier. The hole is drilled at a downward angle to allow the humidifier to be easily installed. The wood has an oil finish.