The problem with the cage is that the hides are WAYYYY to big. Go to Lowe's today and buy the smallest saucer pans (catch the water at the bottom of a plant pot). And when people mean fill the tank with newspaper balls that means FILL it to the lid with news paper. Personally I would just stick him in a 6 qt and save the tank til he starts eating. The tub can be placed inside the tank to keep ambient temps up along with humidity.
To be honest, a hopper mouse or rat pup hurts won't your snake. Feed live.