Hi Troy,
Planet Waves makes a real nice case humidifier, I picked one up a few months ago, found it on Ebay brand new ( typed in Humidifier in the musical instrument catagory) its leak proof, oval shaped, comes with a syringe to fill it, and comes with Velcro so it can be attached where you want it.
It was inexpensive, I have to look through my emails for the price, I couldn't find one like it anywhere else and it cost less than other stores were selling it for if they even had it.
I purchased it cause one of my Conklin 7 string basses started to have a problem, I noticed a small split starting to run up the fretboard underneath the G & C strings, it came out of nowhere, I saw it when changing strings.
I was like how the hell did that happen ?
The person who works on my basses told me it was cause of dryness, I got one of those plastic cup humidifiers with the clay in it, and checked it 3 x daily for days, there was no change, put in the planet waves one in and in no time it was completely gone, it can't even be seen and hasn't come back.
I keep my basses in their cases when not in use, all in the same room, temperature and humidity is constant, I own/ owned many different basses, in my 24 years of playing I've never ever seen that happen to any of my instruments before.
Bruce