I have a T8 divided. You will need a 40w RHP for each side. one won't cut it. Even if I was just housing one snake in a T8, I think I'd either want two 40's or one 80w RHP. If your room was a steady 75+, you MIGHT be able to get away with one 40w, but that's a big maybe.

Getting two 40w's up front is a little more money, but great piece of mind. I like having the two 40w's in mine. Now I have the option of running it as one enclosure, or two.