Leopard Gecko Egg Incubation HELP!!!?

Our Leopard Gecko has laid 4 eggs. The first two were infertile the second two were fine at first then one started to grow mold and collapse inward after about a week. After this egg died she laid her last one and it is starting to do the same I reduced the amount of water but it doesn't seem to be doing any better. What am I doing wrong? We have a homemade incubator. Which is a plastic deli cup filled with vermiculite sitting on top of a sponge on a heating pad (the sponge helps to keep it at a constant temp). There is a humidity Gage inside and it is always around 90% and the temp has stayed at around 80'. What should the humidity be at? And is this setup all wrong it seems to keep the conditions right but my eggs keep dying.