What substrate are you using?
Personally, I'd suggest switching to tubs. I used to use tanks as well but after switching to tubs my humidity stay perfectly steady. I could never imagine using tanks again. Also, 60 gallons seems a bit large for a Ball Python. The 55 gallon tank I have that I'll be using for my boa I'm getting is 4.5ft long. Anything that size is excessive for a BP.
You can also try placing a piece of plexiglass/acrylic over 3/4 of the screen top. That will help much more than a wet towel.