I made 8 or so voodoo tiki torches a few years back. The skulls were cast latex. In the off season they were kept in my porch (no A/C or heat). The following Halloween they were falling apart/cracking. I chalking it up as a loss.
I live in Mass and I've found that some of my props can definitely suffer from the heat in the attic. I started storing things in my basement, seeing as it stays right about the same temperature year round.
Heat in an attic ruins them definitely try storing them in a dry cool place! You can try patching them with clear silicone caulk and then painting it. Worked great for some of my props that I bought damaged!
Just so you know, latex is like 80% water or some crazy number like that, and water evaporates quickly in hot or dry environments unless it is sealed. Once the water evaporates, what's left is dry and crumbly as you've learned.
Since I usually paint all my latex stuff, I first give it a coat of Flex Seal spray rubber to help seal it, and then paint over the flew seal.