A pet store incubator for leopard gecko eggs can be prohibitively expensive and may not work as well as a homemade incubator. If you build your own gecko egg incubator, you have much more control over the size, humidity level and temperature, making it easier to adjust settings and keep the eggs healthy.
Purchase a polystyrene box. Many pet stores or even fast food places will have these boxes in stock and will likely give them to you for free. Make sure the box is large enough to contain the eggs and small enough to fit comfortably into your gecko's tank. You should also make sure the box is stable, because a box with holes or flimsy sides may break and damage the eggs.
Place the heating pad underneath the box. It is vitally important that the temperature in the box remain relatively consistent, so use your thermometer to monitor the temperature frequently.
Select a temperature for the incubator. The incubation heat of the eggs will determine the sex of the hatchlings. Eggs incubated between 30 and 31.1 degrees Celsius will yield males, while eggs incubated between 80 and 84 degrees Fahrenheit will yield females. An intermediate temperature or alterations in temperature will result in a mixed-sex group of hatchlings. Never allow the incubator to go below 26.7 degrees Celsius or above 32.2 degrees Celsius.
Place the vermiculite or peat moss into the incubator. Make sure there's enough of this substrate to cover the eggs almost completely. You'll need to keep the vermiculite moist at all times, but it should never become soggy. Use a mister to mist the vermiculite daily after checking the moisture level. If you're concerned that you will forget, you can also use an automatic mister and set it to mist your eggs daily or twice daily, depending on how humid the cage is.
Place the eggs in the vermiculite. Resist the temptation to pick up and look at the eggs repeatedly. While handling the eggs occasionally won't harm them, constantly rotating them may.
Consider using a thermostat to keep the temperature on your heating pad stable. You should incubate eggs only if you have ample room for the hatchlings and the ability to care for multiple geckos.