Get a 100 watt Ceramic Heat Emitter (CHE) for the Heat Lamp Fixure for a 20-30 gal size tank. The snakes dont like or need light and these are 100% better and they are around $15.
If you want to use the the aspen or other substrate that helps with Humidity you might like it like several others do. I myself dont like wood or the cleaning/smell of urine/feces that seep into it. Some say spot cleaning works good with it but I tried it 15 years ago and could smell the urine in the wood chips and hated it so ive used Craft/Butcher paper. I order 800' foot rolls that are the width of my enclosures.. 12" or 24" or 30"'ect... They last years and you wrap the paper up and throw it out, wipe the enclosure down and replace with another sheet...simple. I spray the sides of the enclosures to raise Humidity if it falls below 50%.
At some point when funds allow, look into a different enclosure. The PVC hold humidity and you can use RHP (radiant heat panel) and hold your Humidity easy with a large water bowl because that isnt a dry heat like Bulbs or Ceramic heaters...
Check out APCAGES. The T8 is on sale $150. Thats what most of us have for Balls. As far as the RHP, check out Pro Product Heat Panels. He is #1 in the business. They arent cheap.. $120 for a T8 size heater panel but will out last any other RHP out there. 10 year warrenty on heat element.
PS- my 3 month old eats Mice twice a week and she is thin and 16". Feed that snake a mouse hahahah