Reptiles are often stoic. I've never seen skin just seperate, was it a live rodent? Could it have bitten him?
A tub is cheap at walmart or the dollar store if you decide it would be easier to move him to a new tub, instead of emptying the tank.
Non-pain relief neosporin only, and I hope he heals up. If it doesn't look like it's healing, I'd definitely say a vet visit.