Bedding plays a huge part in the humidity of an enclosure! What type of bedding are you using?
For my snakes that need a very dry environment I have them on aspen, with just a small half filled water dish, and I never mist. My corns are on aspen but I mist once a day and they have large bowls for soaking in. My garter snake is kept on cypress mulch and I give her a humid hide filled with sphagnum moss.
I'm new to ball pythons but I've had my tank up and running for a few days now and the humidity is at a good level with me using a couple inches of cypress mulch (holds humidity very well) and a good amount of slightly damn sphagnum moss scattered around the tank. I live in Montana and ambient humidity here is really low, but this keeps it up quite well. If you are using a screen lid I suggest covering about 50% of the lid with some plastic wrap or a damp towel. This will also help trap humidity in the tank.
I do agree though that you should get a under tank heater (UTH). And if you get a UTH you absolutely HAVE to get a thermostat. The thermostat regulates the electricity flow to the heat pad to make sure it stays warm enough for your snake, without getting super hot and burning or killing your ball python.
These are the heat pads I use:
http://www.amazon.com/Zoo-Med-ReptiT...s=zoo+med+heat
and this is the thermostat I use:
http://www.amazon.com/Hydrofarm-MTPR...arm+thermostat
It also helps to have a large water bowl in the enclosure and to mist the enclosure once in a while.
If you follow the above directions I can guarantee you will have a great level of humidity in your tanks![]()