The inside of my grill lid is rusting
If you're particularly anal about the looks of the inside of your grill there may not be a solution, otherwise clean the inside as best you can and coat with an oil based cooking spray. Season the inside after spraying by bringing it up to cooking temp (about 350 degrees) without food for about an hour and let it cool. If you over heat the grill sometime during the summer or you live in a particularly corrosion prone environment you may have to repeat this at the end of the season for winter storage without rust.