When you put the saran on just make sure a little bit of each corner is open for top ventilation too (and watch it around that hot lamp). If you can possibly go with UTH (under tank heat) it's really best for the snake and will solve tons of your humidity issues. Those lamps are just terribly bad for drying out the air.

One thing to check is the humidity in the room the snake's home is in. It's a good starting point to know that when you are struggling with an enclosurer environment. Gives you a bit of a starting point and sometimes a small room humidifier really helps (and it's good for you too...humans in the winter suffer too with being too dried out).

The snake may be soaking due to the dry tank but you may want to consider bowls small enough to not allow for this. Misting will help and with the saran wrap all the moisture you mist in there won't immediately dry up. Just don't mist to the point that the substrate is ever really wet.