I just recently bought a Brazilian Rainbow Boa a little over two weeks ago. I also have 1 regular Ball Python. With that being said, the Rainbow Boa is by far my favorite. The average about 5 to 6 feet but don't get as thick. The breeder I bought mine from, his breeders full grown were no more than 5 to 6 feet and about 8 lbs.

That's part of the reason I got one. Also they are beautiful snakes. A little about mine, he's a male, almost a year old. I had him for two days and he ate f/t first try. He's easy to feed, as for his enclosure right now I have him in a 35QT tub in a rack, since he's still a baby. There semi-arboreal, mine most of the time is hiding away sleeping, unless it's feeding time or cage maintenance. But when he's awake, he's like a Boa, all about, curious about everything.

As for humidity, if you get something like Cypress Mulch that holds humidity well, it's not hard to keep. Ideal is about 70%, if you get it in between 80%-90% your ahead of the game. Temps are 85 F for basking, 75 F at night they are fine in.

If you looking at getting a smaller one, the BRB is way the go. Robert Harper as you'll read about in the feedback on sellers forum is where I got mine. He's quite amazing and he's a lot easier to take care of in terms of feeding and temps compared to the ball python I have.

Best of luck!