You need a styrofoam cooler, a heat mat, a thermostat, and a wire shelf from an old refirgerator(or similar) that will fit into the cooler.
Place the heat mat into the bottom of the cooler. You can run the cord out through the top or cut a hole in the cooler. Your choice. Put the shelf in the cooler, using the "legs" that would hold it into a fridge to hold it in place in the cooler by sticking them into the styrofoam. Perfection is not necessary, as it is only meant to keep the lay-box off of the heat mat directly. Use the thermostat to set an appropriate temperature for your eggs to incubate(I don't know what that would be for gecko eggs). Once your leo is ready to lay, put the lay-box into her enclosure, and let her lay her eggs. Once the eggs are laid, place the lay-box into the incubator, and wait.
You should set up the incubator ASAP, to ensure the temperature is reasonably stabalized before the eggs are laid.
Hope that was helpful in some small way. Good Luck!