I also want to stay glass tank. Doing a normal 20 long for now
till the baby BP grows up and do few experiments for heat and humidity. I will always stay glass tank because of where I plan to keep the BP. If I ever need to totally move the habitat I will do a custom build.

I will try to write out a quick thought on moving to a bigger glass tank.

One experiment I want to do is use different wattage bulbs for more or less btu's. Try red bulbs and CHE's to see any temp difference at the same watts. Effects on humidity also. Also placement of the heat lamp on the tank. Over the hot spot/side or more center. I think running on the smaller wattage/btu side will help with humidity and be more even temp. Better regulation and efficiency. 30 x 12 is 360 sq in so I am sure there is a formula for how many btu's are needed. Need to figure that. Then account for the UTH.

I would also like to try a RHE heating from the top? Replace a lamp and be cleaner looking. Not sure if that will even work at all? Not sure yet how there different from a UTH? More research needed.

Another test is size of the UTH. Of course bigger will be needed for a bigger tank. I guess big enough to cover the hot side of the tank? But that might be to big to be efficient. Want to look at that also.

Use a large or even really large water container for max surface area to evaporate water. A pool for the BP. Lol
At worse use a small humidifier on a large tank. But I hope really controlling my heat can help regulate that.

Going to try plexiglass or maybe a foil bubble wrap insulated heating product to seal the top. Some things there to experiment with.

I also will try to stay with a short 12" tall tank. And only so much width as possible. It just seems to me a taller tank will really make heating and humidity trouble.

I think geographical location and home temp and humidity play a role in designing the correct tank habitat. So not every ones is going to match.
So for me once I figure it all out I will be happy as will the family BP. I just want a nice clean looking tank to watch our BP.

Good luck OP and update please on what you buy and how you set it up!