He's in a 20L with two UTHs and a ceramic heat emitter. The room (and my entire apartment) is kept pretty cold, hence the two UTHs and CHE. Two AcuRite thermometers with probes, the ginormous water bowl, two identical hides, fake vines, branches/logs, a rock, etc. He's currently on Repti Bark; the top of his tank is covered in foil and topped with a piece of plexiglass that's just a bit too small to use alone. The humidity isn't atrocious, but I still have to mist the enclosure on a daily basis to avoid crazy fluctuations in the humidity. I'd prefer not to move him to a tub, but if I go out of town or otherwise can't attend to him on a daily basis, I would move him to a tub to keep the humidity in check without relying on a friend/petsitter to take care of it.

Sphagnum moss is also scattered around his enclosure (to assist with the misting) and has also been used in the, as of yet, unused humid hides. If I just stuck a container of the moss in his enclosure (uncovered) and kept it pretty wet, would that also make a noticeable impact on the humidity?

Is the soaking actually dangerous to him, in any way? I know that wet substrate can lead to scale rot, but is soaking in a clean water dish a threat to his health?