Hey Luc,
long time no speak. Hope you are well. I really feel that 82 - 84F is a bit high for z eggs. Simply stated, given their environment, I believe slightly lower temps are in order and those few degress can make all the difference. I utilize room temperature each and every year with excellent success.
Once the eggs are produced I place 'em into a plastic shoe box half filled with slightly dampened coarse vermiculite. I don't bury the egss at all but rather allow them to rest atop the vermiculite, and the box has several quarter inch holes as well to allow for air and humidity exchange.
I then take these plastic shoe boxes (with lid on...) and place them into a very large clear plastic storage bin that is 1/3 filled with water. In this water I have several clean bricks that serve as resting spots above the water for these egg-filled shoeboxes. I place a thermometer probe inside one of the egg boxes and then pladce the lid on the large storage box. Thus, you have small egg-filled shoe boxes resting above an endless supply of humidity inside of a bigger box that holds everything.
Lastly, I use a strip of 11-inch wide Flexwatt (set at 75-80F) under this large storage box to slightly warm the water. With this system I incubate the eggs at an almost-constant 72-75F temperature. Hatchlings emerge at around 80-90 days and look spectacular.
Here's a Cascade intergrade (multicincta x zonata) that may look familiar...

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Jerry Kruse 
"Rrrighttttt . . ." -- Dr. Evil