what size cage will I need in one and on 5 and 10 year.

I am having a blast with my girls "red tail boa and a ball", but because I looking into doing a built in terrarium I want to try to make sure it will last 10 years or so. What I have done so far is divide a 30 gal, works great but I know they will need more sooner or later. The red tail loves to climb, I have never seen her in her hide or anywhere near the floor. So I was thinking or giving her a taller home and put a tall branch in there for her to climb. Once again I not sure what would work maybe 4 feet long by 2 feet deep and 3 feet tall? Would that last her for 10 or 15 years or so?

The Ball loves being on the ground, she only comes out to sunbathe, but I would think she would like more room when she grows maybe even the same size tank? One big question would be how hard is it to heat a 3 foot high tank on one side? Right now I have the tank nailed down to 93 degrees on one side and 83 on the other that drops to 78 degrees at night.
Thanks for the help

Boas get more terrestrial as they get bigger, and they grow rather quickly. A 4x2x2 would work for the boa. I have my girl in a 4x2.5x1.5 and she loves it. Boas aren't agoraphobic like ball pythons are, so they can het moved into larger enclosures sooner. Once our balls hit 2.5 ft, we moved them into 4x2x1 enclosures. It's all black PVC so it's dark and they seem pretty happy. Radiant heat panels are great for heating if you can afford them, and they don't burn off the humidity like bulbs or ceramic heat emitters do. Just food for thought.