yup no kidding mel.
I spray twice daily to maintain humidity, and thats with a generous amount of moss and foil-covering on the screen top.
temec, luckily you aren't TOO high on the humidity, I can't imagine 68% being very bad for the snake as long as the substrate stays dry, since 50-60% is the suggested. It shouldn't be too hard to tweak something and end up with a glass cage with perfect temps/humidity requiring no work to maintain them.
I'm with Jenn, try a different substrate.