We are mentioning what could possibly happen to the snake itself because we are worried about the future welfare of the snake. I am going to wait for the day when you make a thread on here that is something along the lines of this "HELPPPPPP! My snake has a (insert problem here) and I don't know what to do!" Like Kyle said, what are you going to do if something happens to this snake and it requires a pricy vet bill? Could you afford it? Do you have a way to get the animal there? If you were worried about making mistakes, you would take the time to COMPLETELY think this out instead of just getting what you want. What you want isn't always what you need.
The BP you may be getting could have something it could pass on to your other snake. So, do you plan to quarantine your new snake? You say you block off the door to make sure they can't get out. Do you put a towel underneath your door on the outside or something?
Now, my answer to your question is; that tub looks just fine. You can secure the UTH to the tub with foil tape instead of duct tape. Are you going to use a thermostat to control the temperature of the UTH?