Last year I had a little bit of trouble getting the eggs to the right temperature (in the beginning) so what I did is place them in their incubation container, inside a ten gallon aquarium. The ten gallon had a heat mat affixed to the bottom, so the temperature next to, but not directly under the heat mat, raised it up to a nice 85 (I had a temperature probe IN the substrate to measure the temps.)... sometimes it would get cooler, I would move it closer to the heat mat (but never directly ON the mat), and when it got warmer, I moved it further away... until the temperatures got so warm I didn't need the aquarium. By the time they hatched I couldn't keep their temperature below 84 which is good, as outside it was 115+ degrees daily.
Also I don't normally spray the eggs directly, but I considered the situation with the collapsing and imperiled eggs to be an emergency... if you can't get the substrate to help the eggs to be properly hydrate, try the direct method. I would not suggest misting them with any regularity once they are doing good. Once the setup is doing most the work I just add a bit of moisture AROUND the eggs to the vermiculite itself.