Julian wooden cage heating
Julian,
When I got my 4 year old cornsnake he came in a wooden cage with a glass door facing the front (not on top) that locked with a window type lock. There were no air vents and a light
bulb inside the cage. Well, that bothered me as I didn't want him wrapping himself around the bulb and getting burned.
So I took out the bulb and cut the corn on the back. I disguised it with plastic plants.
But to answer your question, I got one of the inside the cage mats that you put under the substrate and they sit right on the wood. My wood is painted white and the inside mat worked fine. I did have to drill a hole for the cord and we put a new plug on it as the plug obviously wouldn't fit through the little hole.
It worked fine for him until I got him a larger tank. I had also cut a hole in the top and covered with screen for some air and a heat lamp that sat on the screen.
After cleaning and disinfecting it, I later used it for a gopher snake that I had for a short time and it worked fine.
So that is what I would do but there may be other ways that people handle that.