Recently, we had a question about how to control rust in and on grills and
      smokers.  You must remember to take care of your equipment in order to keep
      it lasting longer.  One of the best ways to keep your units lasting longer
      is to always remove the ashes.  Ashes when they become wet create a caustic
      base - "lye" - which has the strong propensity to eat up iron.
    
  
  
  Smoky says
  that the best way to prevent this is to clean out all the ashes, hose it
  down real well and spray it with a mixture of 2 Tb. vinegar per gal of
  water.  Let it dry real well. Turn it upside down if you have to. Then try
  to keep the moisture out.   If you use your grill/smoker 2-3 times per
  week, you won't have a problem.