Just out of curiosity, what species do you have and is it an albino?

Putting the hand towel over the top is okay, but I've found that covering the same amount of the screen with saran wrap and duct-taping it in place actually works better, since it doesn't absorb moisture like the hand towel would. Also, if you want to up your humidity you can put the water dish on the warmer side of the tank. You'll have to fill it up more often, but the more water evaporating means higher humidity.