Ah! Finally a subject I know something about
I used a commercial quality (7mm thick nylon) bus tray/tub, the kind used in restaurant kitchens/dishwashers.
Bought it cheap at a restaurant supply house, used it for 25 years and left it behind when I retired. Scrap card-
board always helps as well as a quick steam clean before beginning a teardown on the really filthy ones.
A quick tip regarding oil spots....try to not use brake clean. It can turn oil or grease into penetrating oil,
just what you don't need on porous concrete. Try several applications of Motsenbockers Liftoff #2, available
at Home Depot, as of yet the best I've found to clean oil spots.