Rusty grille - How to avoid

I grill/BBQ almost every day. Over the past 45 years I have had many cheap gas grills, 3 charcoal and one smoker. The worst thing you can do to a grill with cast iron grates is to burn the food off after cooking and not seasoning the grates for the next use. I never clean my grill after use. I clean my grill when I am going to use it and season the grates. However, if you don't cook as often as I do then clean the grates after you cook and oil the grates. I live in a hot humid place so I now have a Weber Geneses III gas grill with heavy stainless steal grates (expensive but worth it). For my 34 year old Weber charcoal grill and smoker every few years I replace the grates. I will not have another grill with cast iron grates. I have also had grills with cast iron burners that did not last 2 years. I do love my cast iron pans.