I live right by Washington, D.C., where we get some of the most humid Summers this side of the tropics. You'd think there'd be no issue keeping your Guitars humidified, but for the fact that everyone runs AC all Summer long, which sucks the moisture right out of the air. I keep a small bucket on my front porch, to catch the drip from the AC, and use the overflow to water the plants on the porch. It's that wet . . .
For my Acoustics, I keep two different humidifiers in the case pick box; a Herco Guardfather, the round one with the clay insert, and a Planet Waves Guitar Humidifier, the kind that's supposed to hang between the strings. They're nothing fancy, basically a sponge in a plastic housing, but they're cheap enough. For my solid-body Electrics, I keep one Planet Waves humidifier in the pick box.
So far, this seems to be working for me, but I wonder if there's anything else I should be doing? I can't really run a humidifier in my Music room, although in Winter, I keep a pan of water under the old-school radiator. FWIW, all of my Guitars live in HSC's, and I don't tend to leave them sitting out of the case, unless I'm actively playing them, so they're pretty well protected.
We're in the middle of a long run of 90-degree+ days, with a heat index of 105-110, and more in sight. 2020 will probably be a record-breaking Summer, which is why I'm thinking about this. We usually get a break where we can turn off the AC and open the windows every so often, but lately, it's just been evil.
Given that we're all in slightly different parts of the planet, not just different parts of the U.S., what are the rest of you doing to humidify your Guitars, and what issues do you run into where you live?