Ok....HUMIDITY.....you're working way too hard on that. Ball Pythons are not "tropical" snakes. They come from arid regions of Africa. We try to maintain the same kind of humdity they might find in their underground homes...which is about 50%-60%. Just bump it up near 70% for the week that they are "in shed" and you'll be golden. So that is one worry you can stop fretting over.

As for the loose skin...I can only say what I've already said. It may take time for him to completely get over the trauma of his trip. And if he's significantly underweight, it will take time to fill out. I still think a trip to the vet would be a very good idea.

I think it's important to know exactly what kind of substrate you're using. "Reddish bark" doesn't mean much. Since humidity seems to not really be an issue, you just need to make sure the substrate is something you can keep clean and it is not toxic to your snake. Pine and cedar are examples of toxic substrate that is fairly common to find in pet stores....so it's a very good idea to know what you have.