I wouldn't advise you to house them together. The red-tail boa is immune to different bacteria, viruses, etc. that the ball python is not and vice versa. They come from different continents and although their temp. requirements are close, boas do better with a more tropical humidity range as opposed to ball pythons, which can do well in a moderate (savanah)type humidity range. Stress is also a factor and plus, snakes are solitary.