I had major issues with this in the winter. Definitely switch to a moisture absorbing substrate, use damp towels or tinfoil for insulation, and maybe think about getting some terrarium moss (they'll sell it near the substrate at the pet store. You can moisten it and put it in the corners of the tank) I've also heard a glass tank makes it difficult to keep up the humidity, so if you think it'll be a longterm thing (say you live in a consistently dry area, consider switching to another type of tank)

1.0 Normal
Normal doesn't mean boring!