First off...the humidity doesn't need to be THAT high, even in shed. If you can maintain it around 50% all the time....that's usually plenty sufficient to promote easy sheds. Bumping it up to around 60% can be helpful during the shed cycle if the snake seems a bit dry to start with. Anything higher than that is just overkill.

Second off...you'll find that maintaining a proper environment in a 40 gallon glass tank is HARD. If you want to continue working with it all the time and putting in the expense and effort it will take to do that....then more power to ya. But I would highly recommend you looking into a smaller, more easily managed enclosure.

In the meantime...try covering the top with a damp towel. Some wads of wet (not dripping) paper towels scattered around the bottom can help as well...just be sure to change them out for fresh ones daily. A good moisture-holding substrate like cypress mulch or coconut husk can help, too.

Good luck with it.