Need help with humidity

I have a ball python, and I struggle so much with keeping her humidity up. She’s in a front open tank, and the screen at the top is completely covered in HVAC tape except where the light is. I do live in a very dry state, especially winter time. Her substrate is a mix of coconut fibers and chips. If I take about a gallon of water and mix it into the substrate the humidity will stay at 70% but then drop to 60 the next day, and then the day after it’ll be right back at 40 or lower. Money is very tight for me right now so please don’t suggest getting a new tank or a mister, but any other tips would be super helpful as I don’t have the time to take everything out of her tank, mix a bunch of water in, put everything back in, and stress her out every other day. I’m sorry for the long read but please help if you can. Picture of the pretty lady for you as well 😁