Heating a custom enclosure

[Ptindy]

Hello. I'm making a custom enclosure for my ball python and a couple other snakes i'm wanting to get. I was wondering, if I use head pads, zoo med, or exoterra, where do i mount these. Under the enclosure floor? Or on the floor under the substrate? The floor will be wood. I'm assuming I need a rheostat for this but which works best? And what kind of heating device would be best for a JCP? UTH or a basking light? Thanks in advance.

MJP