Great question. My 2 cents…
I never bothered humidifying my guitar(s), especially with keeping in a case as to pull it out of it’s case would slow me from playing. I play every day and just love being able to grab my guitar off it’s stand and play it.
I bought a custom guitar hand made for me about 5 years ago and about 4 years ago we went through a severe / record setting drought. Humidity here is normally quite high, 70% and up, it dropped to around 25%.
One day while sitting beside the custom guitar it cracked, wow, and so loud. The luthier said it was due to the drought. While I don’t dispute that at all, it’s interesting my other acoustic guitars, also acoustic and also solid wood, didn’t crack at all. Admittedly both of them are much older, one is 15 years old, the other over 90. He did repair the crack under warranty.
Recently I bought another hand made custom guitar and have been quite concerned about the risk of another crack. Other guitar players have suggested to me that buying from a small shop luthier increases the risk as they don’t have the larger humidity controlled rooms that the larger manufacturers have. Both of the luthiers I bought from make their guitars at workshops on their residential properties. And both are in a quite humid area of the country (sub tropical).
I discussed how to minimize the risk with the luthier who made the latest guitar, a different luthier to the other guitar. I also explained my preference to not keep the guitar in the case every night. The latest guitar was quite expensive for me, cost about double of what the other custom guitar did. It’s particularly delicate / fancy looking.
He agreed with my approach without any stating any strong reservations. My approach is this…
The guitar is kept on its stand 24x7 in our media room which is indoors and sound proofed and insulated to a high level. There is an “R” rating the insulation level has, can’t remember what that is but I built the room and went for the highest level easily available from a local hardware / building supplies store.
i have a hygrometer in the room and it’s been holding at around 65% through this fairly dry winter (I live in Australia). My target humidity is to be above 50%. If it drops below 40% the guitar will go into it’s case at night, which also has a hygrometer, and I’ll use the D’addario humidipak with 2 packs down into the sound hole. I’ll be looking closely at what the hygrometer says the humidity is inside the guitar case when I open it in the mornings.
Like you, I’ve been fascinated by the statements my by others in various forums about humidity and guitar cases. Especially those who simply state you need to put the guitar in it’s case to protect it. If the outside air is dry, so will the air in the case be dry.
Fingers crossed. It certainly wasn’t enjoyable having the other guitar crack as it did in the unseasonably dry weather here.