Hello! I would think the most simple way to bump your humidity would be to move the water bowl to a warmer part of the cage! Also, I switched a couple of my bowls to a more shallow but more surface area bowl which also bumps humidity big time. You could also get sphagnum moss and dampen that (in a container) and place that on a warm portion of the viv.
Also, the light bulb is what is really zapping your humidity; is there a reason why you are using that (since you have a UTH)? What do you have as the top of your viv? Is is mesh or screening of some sort? If so, cutting a piece of plexi to fit over the top of the cage, while allowing non-plexi space for the lamp, helps a ton!!! But really, why use the lamp????
Let me know if this makes sense to you and if I can be of further help. Good luck with all of this- I really think it is the lamp that is causing the headaches!