Are there options for long term cd storage such as cases that are airtight, protects cds from rot, mildew, etc.?

That's a good, and interesting question. Optical media can fail because of age. Pressed optical media can be readable for decades. But burned optical media has a shorter life span. 

Controlling temperature and humidity will help preserve the data. But, it isn't necessarily mold that is the danger. Even without mold, temperature and humidity can cause changes. The metal recording surface can oxidize. 

You can ask banks in the area if they have climate controlled vaults for their customer's safe deposit boxes. (If none do, that could be a marketing opportunity for someone.) 

Store CDs vertically, not horizontally. They should be in jewel cases. Include humidity absorbing gel packs in the safe or storage container.

No matter how well they are stored, there is always the danger of physical damage. This might be the result of accident. There might be a fire where they are stored. We once had a CD drive malfunction, and it scrapped off the top layers, destroying the data.

Because of the possibility of accidents, the best long term storage uses backups. Consider storing copies of what is on the CDs in the Cloud. If you won't use the Cloud, make copies of each CD. Store the copies in different places: Your home, a safe deposit box, a relative's home, your workplace. 

Periodically make new backups copies, and trash the old backup copies. 

I heard about a line of burnable optical media called M-Disk. Supposedly, an M-Disk has a much longer lifespan than other burnable media. The makers claim M-Disk is designed to be readable for one thousand years. But, you need an M-Disk capable burner to write to one. 

why would a CD rot? it's just plastic...

all things deteriorate with time. if you want discs that last forever, try these out:

https://www.mdisc.com/

https://www.nps.gov/museum/publications/conserveog...

if you want LONG term storage look into tape drives.

Wrong category.