As everyone already said, your carpet it not going to help you at all because it holds no moisture. The lights are also killing your humidity.
You can switch to aspen, cypress, or eco-earth, I mix my aspen with eco-earth(about 40% eco to 60% aspen).
The 46 bow, I believe has a smaller foot-print than a 20 long just because it is so tall. So you should be fine with the tank, just make sure you have a couple hides and some other clutter in it so that your snake feels more secure. I use a bunch of the fake suction cup plants in my 55 gal. to cover the whole back wall.