for snapper eggs I used a 5g bucket, 1g ice cream bucket, water, mulch / soil, and a clamp lamp.
Put the eggs in the ice cream bucket with mulch / soil mix (or other prefered substrate). Then place that inside the 5g bucket. Add some water into the 5g. Then clamp on the lamp so it shines into the buckets. the heat from the lamp will incubate the eggs and create humidity from the water. This should work with many hardy north american herps..... it worked great for snappers in Michigan.