With as much rust your ash pan has, I would be cautious about sand blasting it. The powder coating/sand blasting place I use has told me that sand blasting always removes a small amount of the metal in the process. This was the ash pan from my 57-58 Custom kettle.
I didn't sand blast but used multiple applications of Evaporust on my ash pan. It removed all the rust but I ended up with holes in the metal because the rust damage was so bad and deep. I think you could end up with much larger holes if you sand blasted yours. You can see the holes in my ash pan towards the middle of the pan. Even my front leg has holes due to rust damage. The legs also were soaked in Evaporust.
I believe the ash pans originally were painted, not porcelain enamel. (*The below photos are not mine but were sourced from a kettle on a Ebay auction.)