Hammer,
I live in Colorado and so far I haven't had to use a humidifier with my Series II (it stays in a flight case), but I do use one for my Vintage 62' reissue Hofner, which is hollow body and prone to checking due to dry conditions. I use an Oasis Case+ unit with the Digital Hygrometer so I can monitor the humidity level and temperature in the case. The Case+ unit is designed for extremely low humidity levels, and puts out 50% more humidity than their standard unit. Works VERY well (humidity levels hang at 40-45%...BUT you have to refill it about every 3-4 days. It attaches to the inside of your case by a magnet...
Not expensive...most all retail music stores carry them at about $46 including the Digital Hygrometer, or about $20 for just the humidifier.