BPs are nocturnal, so seeing your snake out cruising in the evenings is normal. You can take some steps to try to maintain humidity in the tank, but IMO, once you try the tub and find you never have to mist or mess with it at all to maintain humidity, you'll wonder why you spent so much time messing with the tank...
Cypress is usually pretty moist straight out of the bag, but after a few days it will dry out and the humidity will drop. You will eventually have to start misting again, although I've found cypress to hold humidity and moisture much better than aspen... I'm running tubs with paper towel substrate and have no humidity issues at all...
Oh, I also wanted to mention that while it was stated in a previous post to make sure you put holes in the lid of the tub, that's not necessary at all. I've never had a single hole in the lid of any of my tubs and have never had any issues. Just add more holes in the sides of the tubs until you reach desired humidity...