I had a bad experience with using only a humidifier to keep my bass from cracking, and dampits seem to have saved the day. My switch from humidifier to dampits was done with the recommendation of David Gage, one of the top bass repairmen in NYC. A few years ago I had been keeping my bass out of its case and used a cool mist humidifier, diligently refilling and cleaning for quite a while. But after a few cold weeks in January the side cracked. I took my bass to Gage and asked him how I could prevent this bearing in mind I had a humidifier going 24-7. He told me that if you have a large dry room with a lot of wood in it, the room can suck up most of the moisture with very little or none left for the bass regardless of where you put the instrument and/or humidifier. He suggested I keep dampits in the bass and the bass in its case where only the bass will suck up the moisture. I have done this for a while now and it seems to have worked well.
Then I read the comments by Jeff Bollbach. It makes me a bit nervous.
Originally posted by Jeff Bollbach on another thread
If you were to wring out a wet dish towel with all your strength, until not a drop could be wrung, then hung it by an end-a puddle would soon form underneath due to gravity and capillary action.
And
Spray a water bottle on a flat surface at 30%, come back in 3-4min. and it'll be gone. The water in a well-wrought dampit is less. The dampit was a good idea at the surface level but it just doesn't hold up to real physics.
Im not sure I fully understand this. If the water sprayed on the wall from the water bottle disappears in 3-4 minutes then how could the water in the well wrung towel (or dampit) hang around long enough to form a puddle? I often leave damp (sometimes pretty wet) clothes around to dry and no puddle forms. Doesnt this all depend on the level of humidity in the room and what is there to suck up the moisture?
Luckily, this may not even matter. The dampits I own (as well as any Ive come across) are encased in rubber with small holes along the side to allow the water to escape. I also glue the bottoms of the dampits to their sides and store my bass upright so Im not sure how water could escape through the bottom.
And there are a lot of scenarios where basses must be kept in their cases. Way back when I was in school the only place to store our basses was in a bass room or locker where humidifiers werent plausible. Im sure there are many reasons to keep your bass in the case, and many situations where it is a necessity. And, of course, there is travelling around with the bass, which has already been mentioned.
I do try to use a humidifier to keep my apartment from getting so dry, but this is as much if not more for my health as opposed to the health of my bass. I have a couple of dampits that I wring out pretty well before putting them in the f-holes. I usually change them every other day or sometimes every day if its really dry. This has worked for a number of years my bass has not cracked since!
Paul Bollbach and Arnold Schnitzer are experienced and respected luthiers. But I seem to be having a very different experience with dampits
(100 degrees, 100%), and the bag can only help so much. Gotta run to the old Dodge van and crank the AC!! 
