You are trying too hard to clean that. There is no reason to get that back to shiny. I don't "clean". I cover the wood box, bottom of the smoker, and catch pan with foil. After a smoke, I scrape excess grease out of the bottom with an old plastic credit card, then wipe with a paper towel. If there are any loose crusty bits on the walls or the inside top, you can lightly scrape with a plastic credit card or plastic putty knife. If you really want to clean the top of your wood box, try oven cleaner. The top of my wood box is black, even after covering with foil. The top of your wood box will never be shiny again. It shouldn't be. The black on the walls of the smoker are seasoning. If you need to get your smoker that clean, you will probably never use it. It is impossible to do, not necessary, and is not desirable. If you want to clean and re-season every few years, that's okay if it makes you feel better.
I soak the racks and rack guides and put in the dishwasher, and that's about it. I'm not sure how necessary that is. Especially the rack guides. I don't think they need to be "cleaned". I line the catch pan under the smoker with foil, so never really need to clean that.
