Just a quick update:

I placed aluminum foil over the top of his enclosure, and that's been keeping much more humidity in.
I also managed to get him to eat a bit of food, probably about the size of a large grape. I'm going to feed him again tonight and see if he eats again.

He's also started calling again, so I think he's a bit more relaxed than he was a week ago. I'm still paying close attention, but I hope this is a sign of things moving in the right direction. Thanks everyone! : )