You came to the right place.
If you have a screen lid, I would cover 3/4 of it with foil/plexiglass/wet towel to help with humidity.
How are you heating? If by lamp, it could be sucking out humidity too, and UTH on a thermostat are best.
I don't know about the dent, but it sounds like something that could be caused by dehydration.
If you do those quick couple of fixes, it should help, if you don't already do these things. I'm guessing you had one of those dial hydrometers and those are not reliable. I would grab up a digital one, normally we recommend the accurite indoor/outdoor temp/humidity gauge that is available at most walmarts or lowes for about $13. You can do a search and read up more about that if you'd like.
About the food, this maybe be because he is adult size and it is breeding season. The weather is getting cooler and the snakes are going off feed (not all do, but it is common).
Good luck, and hope I helped some.