What kind of heating pad are you getting, human or a speciality reptile one? I would go with a human heating pad. I use human heating pads, and leave them on all the time. As for the gap, i think its almost necessary to get your temps good if you are not using a thermostat. It also provides a bit of security incase you bp decides to burrow under the substrate. Then he will not be in as much contact with the direct heat coming from the pad.