Yeah, tubs are great but you are running into problems with your tub set up also. The way I see it is this: There is no one solution for every situation and it really depends on a lot of external environmental factors.
My solution, since I live in the high desert where it is always cold and very dry, was to cut my losses and frustration at the get-go and just go right to enclosed racks and reptile cages. When it became apparent that flex watt was not going to be able to raise my ambient temps enough (in the cages) I switched all the cages over to RHP's- problem solved.
In the winter time I need to enclose all racks and cages with rigid pink insulation since we keep our house cool in the day and even cooler at night. The insulation works and solves the winter time problem.
For our terminally low humidity, I keep a bowl of damp long fiber Chilean moss in all of the cages and throw a very small amount of it into each of the tubs in the four racks every week or so- problem solved.
So, it really depends on each keepers unique external environment that will determine the best housing conditions for their snake(s)![]()