on the big cheifs when it got colder out I'd slide the box that the smoker came in upside down over the smoker with a couple of cutouts where needed to add another pan of wood and let the smoke out the top.
the cardboard box insulated the big cheif pretty well and it kept the temp more stable.
I've been temped to make a cover box for the big cheif out of pine or some other soft wood, or just scrap the metal and make a wooden box that will fit all those racks nicely, could even make a nice damper on top to control the smoke. I'd also scrap the coil and go for something with a temp control like a hotplate
hell all I'd have left from the big cheif was the racks