Any chance of just getting a new tank?

Is the duct tape inside or outside the enclosure? If it's inside, you need to get it out immediately. Snakes have an extraordinary talent for getting themselves stuck on tape...ANY tape that they have access to. And when they do, the results can be very, very bad. If the tape is on the outside...then that means the cracks are still exposed on the inside, which lead to a risk of him cutting his face when he pokes around and rubs on his enclosure.

Of course, the "wall paper" that you're talking about can help with that...IF you can figure out a way to affix it to the inside of the glass without using any tape. Pet stores sell such papers and they don't cost much...usually desert or underwater scenes. Maybe glue it on and make sure the glue is fully cured and not fumey before you put the snake back in.

The problem with the wall paper on the inside of the enclosure is that it might be a pain in the butt to clean and could get really nasty if the snake chooses to lose a big pile right up against it.