temp guns are always good to spot check. The can be useful for measuring temps of different areas of the enclosure very quickly if anything does go wrong. Quick check the bottom of the tank, quick check the cool side, check the animal's skin itself. It's very useful and always good to have an extra source of accuracy to check against your thermometer!
also do you know if an 8watt UTH is enough for a 20 gallon long?
I was wondering something similar, I have a 2gal uncycled tank and was thinking of purchasing a 9w under tank heater (nor submerged) will that be too hot for my tank or too weak? there is a small layer of marbles on the bottom (bout 1.5 inch or less) and I was going to wrap the heater in a towel to protect the glass from over-heating as well as my counter. I have a thermometer on order so I can moniter temp