I have put rats in the freezer with the food. Now I feed live. I found the foodsaver vacuum seal bag are good for rats, no freezer burn and they can be frozen individually or in groups, depending on your needs.
I only freeze em if I have a surplus. I try to manage my rat colony so I don't have to many rats.
They are in their own freezer now. The wife and daughter hated having them in there no matter what. I'm sure it's safe to do,(rats and food together) but it is kinda creepy.