Vypyrz, that my friend is a brilliant notion!
I think it is hard for them to move the tub but jbean7916 has had one do it. In general I'd say tubs are harder to secure than enclosures. My concern with the rack isn't (or wasn't... :O) that the snakes would push it out, but that small hands would pull it out.... All my enclosures are locked with a key, the key just at the limit of my reach out of sight (I am 6'4" and can reach 8')
I have never yet had an escapee but I have a good friend whom lost 18 snakes in one day from his niece visiting and wanting to look at the pretty animals... when everybody was focused on the new baby upstairs. It sounds stupid but his kids understand the house rules about the snake room but his sisters didn't. That is always my concern with a rack, luckily I don't have many small visitors and my rack is in a room I keep closed and I have a child proof door thingy on it after my friends experience.