I use a old comforter from a king size bed. Been meaning to line the bottom with a welding blanket, but it works great for my smoker. I cut out the areas where it goes around the counter weight pipe and exhaust. then sewed the seams back. Works great and looks custom made (which it is I guess). The smoke has turned the back brown in a several places, but I could care less.
Damage BBQ 250gal offset reverse flow homemade smoker on 5x8 trailer named #2.