I've read the most recent updated patch and love the idea of upgrading tiered containers. Quick suggestion would be an option to enforce adjacent tiers so you can't skip from tier 1 to tier 8. Gotta make us work for it!

The fridge "Cooler" doesn't cool stuff and it seems that part of the container isn't defined in the function somewhere. A photo below.
https://imgur.com/a/GBsEjGc

The freezer and fridges does not have an "upgrade" option. So they're stuck at tier 1.
Cheers!