Bring them inside. When I was raising them, I gave them nothing but wheat bran. I used a plastic wallyworld storage container, cut a hole in the lid and screened it. With nothing but wheat bran, no smell, no fuss. Are you sure they are dying, or maybe just pupating?
Put the "dead" ones in a separate screened box with a few scraps of cardboard and some wheat bran, they will probably hatch and start laying eggs to keep you in business.
Ok, I will bring them inside. It must be the heat. I'm certain they are dead. We haven't had them but about 5-6 days and the ones that were black and soft a few days ago are now black and hard. So, they are dead. Ugh! Thinking I may have bought too many also (2000). I also have mine in a Wallyworld clear plastic tote. It's long (36") and narrow(13"), but not very tall (about 6").