I've done it before both ways... with a pot and just with soil in the tank.

With a pot: Just put the pot in a corner or a couple pots in a couple corners and put the mulch around the sides to make it stable. My juvie haitian boa would curl around the plant in the pot (I think because it felt secure there).


Out of pot: You could put a few inches of soil in the bottom of the tank (this does wonders for helping humidity), just make sure there aren't any additives (fertilizers, chemicals, etc.). Then plant a few plants. Your BRB won't be able to climb on them, but they'll provide cover and humidity. You can also cover the dirt with mulch, just watch for mold. I've done potted pothos with Sibon (they loved to climb on it), GTPs (good cover and I also provided climbing branches which the pothos will grow on), and with ATBs (same idea as GTPs).