Ideally you want a way to measure temperatures on both sides of the enclosure, at "snake level". The humidity gauge should be on top of the substrate to measure ambient humidity levels.
If you only have one thermometer, put it on the cool side to measure ambient temperatures then buy an infrared thermometer to measure surface temps on both hot and cool sides of the tank. Alternatively, you can buy a digital thermometer/hygrometer combo that will measure temps on both sides. (I would especially recommend this if your current thermometer/hygrometer is a dial analog type. These are notoriously inaccurate)
Heat tape is also known as an under tank heater (UTH). It is used to provide a safe, warm basking area. Heat tape puts heat directly where the snake is resting. It is preferable to typical heat lamps, because it won't drain humidity. A UTH MUSTbe regulated by a thermostat. Without a thermostat, heat tape may get too hot and burn your snake. However, with a thermostat, heat tape provides a steady and reliable source of heat.
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