The following was in the January, 2003, issue of Skinned Knuckles. How you store a vehicle is critical to its well-being. Storage under plastic sheeting is a particularly bad idea. The same feature of plastic that protects things from falling rain and dust traps moisture that rises from the ground. Unless a vehicle is parked on sealed concrete, putting a sheet of plastic over it will do much more harm than good. Cars can be ruined in just a few years of storage under plastic sheets.
Another problem with the plastic sheet treatment is that many plastics, like polypropylene sheeting, are extremely abrasive. They will abrade, and even destroy automotive finishes. “The best storage for old cars is under cotton sheets in tight, heated buildings with sealed concrete floors. Even in those high-class car storage digs, it is still a good idea to place sheets of plastic under cars stored for long periods. This helps to prevent moisture from attacking their undersides and protects the concrete from oil drippings.”