Humidipaks are not quite cheap, but by far the most convenient way to bring more humidity into the guitar case. Not only during the heating season, I do not begrudge my Takamine this little luxury, and it seems to thank me with a better sound (and to quote a friend - even if the sound is subjectively better, it does the job ;-). Mich frightened solutions with water. The size indicated on the pack service life of 2-4 months, I have been clearly exceeded (exchange only if the packs are rock hard). Measurements with a real hair hygrometer showed effect (besides the head-Pak to reach 51% during the Winder season, which is very good) - but the most infallible sign of their effectiveness is that I have the guitar hinunter- instead up vote must - which is, that the wood expands slightly. I think every Acoustic Guitar earned the!
Tip: Essential is a good closing guitar case, which is often overlooked, because otherwise the room humidified, but not the guitar.