81 degrees is pretty darn high for cresties. You might hatch some eggs, but hatch rate goes down significantly over 76 degrees. They also hatch out much smaller.
Cresties incubate at a lower temp than most snake eggs, as they are usually buried a few inches under soil in new caledonia, not in a nest and incubated by a female for months.
Many people incubate as low as 65 degrees. I prefer a warmer temp for faster hatching (I really don't like my eggs taking 150 days to hatch) and I don't use a heating or cooling element, so 74 (aka my room temp) is my chosen incubating temp.
Did i ever state to incubate cresties at 81. I merely stated with a temp controlled room you can have a 100% success rate as i did with my corn egg incubation at room temp. When incubating at a controlled room your only worry would then be humidity in the tubs.