John j, A rotissary is a framework that you bolt the bodyshell to so it can be turned over to access the underside for ease of repair. These are usually only used in restoration or fabrication (hot rod) shops, as they generally require the body to be stripped bare and seperated from the frame, if there is one( and no other type of shop cares that much what the bottom of your car looks like) It works just like the "chicken" rotissary, just on a larger scale.
I used a twin mattress. Cheap, disposable, worked great! Just not quite as slick, and not fireproof.