Vegas climate can be difficult for sure.

You made the right step moving to a tub, as tanks are near useless here in S. NV without a lot of extra work... Covering the top with plexiglass keeping about a third or less open for ventilation, misting daily or using a room humidifier or reptifogger are a few possible fixes.

The 105 qt is a bit larger than needed, and you might have gone too far with the 30 holes. It is a much bigger tub than i am used to, so not 100% on that.

I currently run cb70 (37 qt I believe) racks for my adults with 18 holes, and still have issues with humidity. I have resorted to a whole house humidifier in my snake room keeping a constant 55 percent. When it come time for shed, i slide their water bowl toward the hot spot to bump it up to the 70+ . Works great, but probably overkill for one BP.

If you want to keep the larger tub, try covering up a few holes and keeping an eye on the effect to the humidity. Shredded aspen should be fine; however I prefer unprinted newspaper. Either way, I think you will find some type of humidifier a necessity here.

Best of luck, and feel free to message me if you have any questions, or if I can be any help.