Thanks all for the replies! I posted the photos on my Morelia forum, and somebody suggested he'd been chillin' on the cool side... that was probably true due to the placement of his tub, so I moved it around to where the hide is directly over the heat tape. He's been in there on & off for the last 2 days, and the lump does seem to be getting smaller. He also passed a urate last night, which seems to have helped his swollen belly as well. I'll give it a few more days, and then call my vet if there's no more progress.