KMG pretty much gave you the advice you need.

If you want to try and raise humidity without misting constantly, try moving the water bowl to the warm side. Aside from mites, if they soak it could be a sign they are getting ready to shed or they are too hot.


Also, you can upgrade to a 40gal glass enclosure or equivalent as you said, after he is eating better. I'd recommend a PVC cage. They hold humidity an temps very well. I keep most of my snakes in a 3x2x2.

here are a few brands to consider if you decide to go that route:
visions cages
boaphile
pvccages.com
animal plastics