I know it's possible, as an NPC is already doing it in Northwatch Keep, but when I place a custom NPC in a custom cell, they refuse to sleep forever as I want them to. I intend on making them a snack for my vampire to pop in and grab a bite. I popped into the CK and looked at that specific prisoner, but outside of building and placing things, I don't really know what the hell I'm doing and I didn't see a script attached to her or anything that made any sense to me. x_x Thanks in advance. ^-^

when you make a sleep package for that NPC, uncheck the interaction flags, and leave the ignore combat flags checked

basically if you want to the npc to sleep like a zombie, even through a magnitude 10.0 earthquake, you can copy the MannequinStay package, and set it to Sleep instead of Travel (or you can just copy all of the mannequin package flags settings).