Thanks for the advice, guys. It's a digital hygrometer alright, and no, there's no screen. I've actually recently added a second water bowl, so there should be plenty of water surface area. One is right at the warm end and the second is more towards the middle. This got the humidity up to 60% on the cool side, but the warm side still rarely gets much above 30%.

I've had him now for 6 months and he used to be quite active, spending some time in each of his hides. For the last couple of months, however, he's barely left his warm hide. It's like he knows it's winter outside, even though his temps have remained stable the whole time. He is eating consistently, so that's good I guess. I suppose I'll keep the humid hide in there for the moment anyway.