I wasn't happy with the little Oasis dehumidifier velcroed to inside of my case. It would dry up too quickly and didn't stick well against the case anyway.
So, for my best ukes, I chose the same stuff used to climate control cigars, Boveda. The company makes dehumidifier packs specifically for wooden music instruments. They're not as cheap as the small dehumidifiers, but I haven't regretted my purchase in the last year.
Requires two parts: