When my wife and I first moved to the Philly area from Orlando we didn't consider how hard the winters would be on my guitars. I watched a guitar buddy place an elongated sponge style sound hole humidifier in his acoustic guitar when storing in it's case. I began doing the same thing, but still experienced bridge cracking on my Taylor 414ce. Why had this happened? Many times when I re-wet the sponge I found it was completely dry - and after only about 2 weeks. I speculated that going from very high relative humidity to a level below 20% RH, at times, had been very stressful on the wood and may have contributed to the damage. I was also experiencing fretboard shrinkage, where the fret wires were noticeably extending out from the neck. This was very annoying when performing licks up and down the neck. These issues caused me to question how case humidification helped the entire guitar. So, I purchased and placed a series of hygrometers inside the case with a variety of humidity sources, and quickly observed variation sometimes as high as 28% RH inside the case (top to bottom, side to side, end to end).
There had to be a better way - one where I could also display my instruments instead of hiding them away in cases.