I would use the heat lamp during the day for a thermal gradient of 75F to 85F under the light. You could then put the mat on the wall or ground on a thermostat to come on if temps drop below 68F. If you use it on the bottom then reduce the substrate to one inch or less. A deep substrates is not needed unless you're going for a bio-active tank with drainage layer and a few inches deep for planting. This is best done in a tanks 24" high since the layered substrate will waste available height to the frog