rustNow that I know about it, it seems like a no-brainer. But, I had not thought about it before.
I met a team over the weekend that was cooking on a 60. It was about 8 years old and was in really good shape. They told me that they had quit trying to repaint it (especially the firebox) a long time ago. Even with the highest heat resistant paint it still chipped, cracked and would rust. They would just spray Pam on all the really hot parts when they were done.
So, I'm cleaning my 48 today. I've only had it since May but already have a lot of pitting which led to a lot of bright orange rust. This is caused by the fact that I put wood on top to warm, and during competitions will put pots with sauces/bastes to warm.
While the box was hot I poured some vegetable oil on the surface of the box and rubbed it in with a paper towel, much like you would an iron skillet. The oil set in and the rust is gone. I will be doing this at the end of every cook to protect the look of the firebox.