Yeah it's a bit surprising that it's being used up that fast, especially in an enclosed environment... the fridge is well-sealed, right?

My 1.2 gal humidifier in a 24 cubic ft stand up freezer only needs refilling every week or so, and that's with a 4" hole and a fan going on for 15 minutes every other 30 minutes. But, my chamber is in the 55 degree basement, so it literally never cycles on (therefor, humidity isn't as quickly removed). Plus it is pretty full of meat, so that will help.

And now that I type that out, I wonder if that's your main problem, the fridge isn't full enough. When it has a lot of product, the volume of plain air is much lower, and the drying meat adds to the humidity. So the humidifier doesn't have to work as hard. But not in your case.

Regardless, I'd upgrade the humidifier, to something like this Vicks one I currently use with 1.2 gal capacity or this Crane one that I used to have (which worked fine, just wanted something a little bigger), or this huge unit from Honeywell which might actually be too big. Remember it MUST have a switch or a dial, because it needs to come back on when the power switches back on. Push button controls tend not to do that.