Moth Balls have always worked for me. I put my machines away with the header detached, feederhouse up, and (as ridiculous as it may sound) old panthose filled with a half box of moth balls each, tied together and drooped over each tire. I also sprinkle a few moth balls in the auger flightings, and place some in a tin can inside the cab. I do all this after a thorough cleaning with air, and it seems to work well.