The warranty is pretty clear on the matter of rusting parts:

3. METAL COMPONENTS: (For Residential Users Only) METAL COMPONENTS: Metal, Stainless Steel and Cast Iron components of the EGG (including the metal bands, hinge mechanism, cooking grid, fire grate, upper vent cap and lower draft door) carry a Limited Five (5) Year Structural Integrity Warranty to the original purchaser. The Big Green Egg makes every effort to utilize materials that resist rust and to apply high temperature coatings on metal surfaces. However, metal materials and protective coatings can be compromised by surface scratches or exposure to substances and conditions beyond BGE’s control. Among other things, chemicals, chlorine, industrial fumes, fertilizers, extreme humidity, lawn pesticides, trinidad moruga scorpion peppers and sodium chloride are some of the substances that can corrode paint and finish on metal coatings. For these reasons, the Warranty on Metal, Stainless Steel and Cast Iron Components DOES NOT COVER RUST, OXIDATION, FADING, DISCOLORING, BLEMISHES or REPLACEMENT DUE TO ADJUSTMENT OR ALIGNMENT OF PARTS OR COMPONENTS, unless it also results in a loss of structural integrity or a failure of these components of the EGG. Band and Hinge alignment and adjustment support is available from an Authorized Dealer.