CharlesMTF, I started with some practice plant-only terrariums too. I also experimented with a planted tray that I could insert in the snake enclosure, but also remove if the plantings didn't work out (those first ones didn't - one thing I learned was that the King would just bulldoze under any moss I had growing).

There is another current thread that comes and goes about bio-active. If you haven't come across it, it is worth a read too. The short form is, IMHO, a min. one inch bottom drainage layer is absolutely necessary (gravel, leica, hydroballs, or matalla filter covered with regular fiberglass window screen), and also, spend the money for a quality substrate to plant in. Garden soil and compost are good amendments for the substrate, but should not be a large portion of the substrate. You really need an ABG (Atlantic Botanical Gardens) type of light fluffy mixture. I like NewEnglandHerpetoculture's version. That will probably be the most expensive part of the build.

I would build this with the MBK in mind, not the BP. That said, I know of at least two other members (active recently??) who have BP's in planted enclosures. One person, I can't remember, but IIRC, Snake Judy is the other.