So the answer you seek requires us to ask more questions? What is your humidity at in your tank? What is the temperature where your water is? What is the temperature where the skull is? Where is your "heat mat thingy" or under tank heater UTH located? Is your UTH regulated with thermostat?
Take that heat gage out of your tank now. It sticks and your snake can get it off and stuck to him when he climbs on it....and he will climb on it.
So to answer your question requires more info.
We we are trying to help you and your snake.