And all your incubator vents are plugged up?
Heat alone shouldn't be causing you issues, but if your air is particularly dry, then you're going to have to keep adding moisture to the environment. You can try to provide more surface area for evaporation, a wider water source or even a facecloth with one end in the water, but you're always going to be refilling the water if you have dry air sapping the moisture out.
Some folks do a dry hatch, but I've never personally tried, so I can't provide much information on the concept.