I use al kinds. The easiest is to set aside a room for inverts and keep the whole room at the required temps. I also use heat pads, (placed on the side) and heat lamps. Both work best if they are used with a thermostate. Both will dry out a tank.
Heat pad under the tank is definetly not a good way to heat.
Why? : Scorpions dig some burrows when they want to reach a cooler temperature. So heating under the tank don't let this possibility.
The appropriate heating is always by the side of the tank (above the substate) or by top. The heat has to be transmitted by the air, not by the substrate. Compare it with the natural environment and you will understand it very rapidly!
The best way to heat a tank is by side with a heat-cable.