Looks like a blister to me...don't pop it, but if they spread (become more numerous &/or get bigger) you might need an experienced herp vet to see him as it
could be some sort of infection (or some other internal abnormality) needing treatment. Let's hope it resolves on it's own, just keep an eye on it.

Probably a waste of antiseptic as it doesn't appear to be any break in the skin. But it would be a good idea to be keeping him on white paper towels (with no
organic substrates) until you know where this is going. Paper towels will help reduce chances of infection, but won't help with humidity.