I'm gonna be the bad guy and tell you to can the 55gal bc unless you have a snake room where temps/humidity are always up your never gonna hit the spots you need... I tried for about 2 months to get my 60gal to work and couldnt do it with every trick in the book... Tried plexiglass over the top, larger water bowl, reptile humidifier, 150W CHE, 2 UTH's... anything you can think of... I dont wanna rain on your parade its just too much empty space to heat up. I even moved my CHE into the tank and it got my temps where it needed to be... but killed my humidity. You can try all the things brimstone suggested but my bet is on you not hitting your marks. Best bet is to either build a custom cage big enough for both snakes if you insist on keeping them together or buying a plastic cage.