I've seen one for acoustic but short of running a room humidifier (I've got electronic stuff/recording gear in the same room that shouldn't be humidified) is there one for my guitar in the case maybe?
Planet Waves has one but I'm not sure if it's just for bowed instruments or not. I need something, my fret ends are sharp with winter here and It's very cold and dry and humid in summer, so radical change climate. Wish I could have my own custom made non wood guitar, but until I get rich I'm just going to have to deal with wood's instability. Please help.