Firstly, do not drill the holes. Drilling leaves sharp edges that could harm your snake. Use a soldering iron if you can, a wood burning tool works well to. As to where to melt the holes, I think that is personal preference, but I could be wrong. For what UTH, I would recommend getting flexwatt heat tape. And IMO paper towels or newspaper make good, easy to clean substrate.
but this is all just my opinion. I'm sure a more experienced user will steer you better than me.