If it's during a shed.......then 75-80% on the warm side of the tank. I try and give mine a bit of a dryer (55-60%) place on the cool side just so they have the choice of a lesser degree of humidity, but still there is sufficient amount to assist in a molt. You can acheive this by only spraying down your substrate (if you use bark or mulch) only on the warm side, and providing dry newspaper on the cool side. Since you've been instructed to use newspaper or papertowel to help with the scale rot, then get some everyday moss that you can buy in a plastic bag at the pet store.
soak it in warm water for about a minute, squeeze it out and roll it in paper towel...squeeze it in the paper towel lots and lots and then put it in the hide with the snake to maintain a high humidity in the place he spends most of his time. Don't put it under him, just beside him so it will give off moisture and he doesn't have to lay on it. His rot should improve greatly after this shed and then probably go away after another shed if you keep him in proper conditions. Your snake should never feel wet. His skin should alway feel dry to touch, even at 75% humidity, his skin should be dry. His surroundings can feel moist, but not him. If you put the moss in with him in his hide, then twice a day, check the hide inside for condensation that may drip on him.....wipe it out as often as needed to keep him feeling dry. You should have a heat source UNDER him on the warm side to promote warm humidity. The moss should dry out in the hide about every two to three days. You can fluff it up and turn it over after day one to let all the moisture out of it. Moss is very mold resistant and should help maintain the humidity in your tank. You can even put some out of his hide over or by a heat source so it evaporates warm moisture. This is the best kind of moisture to have and should be the only kind of moisture that your ball python is exposed to. Cool moisture causes pneumonia very quickly as it lowers their body temp and they become very suseptible to infection. You may have to spend a bit of money on this guy to get him set up properly, but once he's happy and set up, he will be on the mend before you know it. These guys are pretty hardy fellas. I have a girl right now that has really bad retained eye caps from her previous owners (I've had her a month). She is almost blind in her left eye and her right is going as well. She is an older snake, but it will take a trip to the vet to get her eyes working for her again. I can see her pupils through the skin still,so that's a good sign that she's still trying to focus and see through the caps. I will have to spend some money to help her out, but I love her and I don't mind doing it one bit. Hopefully you will grow to love this little guy too and it will become an obsession like it is for most of us on here. All snakes deserve a loving, caring owner like you and I and most others on here. It's unfortunate that this snake of yours had to suffer to get to the state he's in, but with some time and tlc, he'll make it and be happy once more. Great job and keep up the good work!!
Cher