Don't use wd40, it will kill the primers and I wouldn't advise keeping them in plastic bags because you will trap moisture in the bag. You wuld be better off with a paperbag or cardboard box. All the shells have steel heads, some are coated with a thin layer of brass. You can clean as much of the rust and corosion as you can and give them a very light coat of oil then wipe them again and store them but I would try to shoot them asap because once rust starts it will continue.