I know you can place unconscious bodies in trashbins in order to have them not count as kills, but does any elevated surface work just as well, i.e. tables and bathtubs? I stored an unconscious body in a bathtub and came back and it was gone, so wasn't sure if it had been eaten or just disappeared.
I cannot vouch for any elevated surface (having not tried every one in the game). But in general yes. As long as the body is off the ground the rats cannot get to it.
As for your disappearing body I do not know exactly why that happened however I noticed it in my game as well. And not just bodies left in the open. If you store bodies in trashbins and come back later they will be gone (sometimes). It seems like bodies just time out after a while.