I agree with redshepherd. Balling up or not balling up isn't a big deal. Some snakes do and some don't. Another way to keep in humidity is to lightly mist the tank and then cover the top with tin foil. I'm currently using paper towels over half the top of my tank, I spray them once in the morning and again before bed, it keeps the humidity between 60-70%.

Also, you said the tank is between 75-85? That's fine for ambient temps but your snake also needs to have a "hot" or "basking spot." The temperatures on this spot should be around 88-91 degrees and cover about a quarter of the tank. If you don't have a hot spot for your snake they can become sick and have trouble digesting meals. You can create a hot spot by buying an under tank heater and a thermostat to set the correct temperature for your snake. You can buy both of these on Amazon.com for under $100. Search "zoo med under tank heater" and "Hydrofarm Jumpstart Thermostat".

If you already have all of this set up, sorry, I just thought it was important to mention