I am the guy who says dont get the insulated firebox and spend the money elsewhere
I live in Michigan and dont miss it. Paul generously donated my smoker for our charity BBQ efforts and it does not have it, but knowing what I do now after using it all winter I would not get one if I was to do it all again. He made the pit to my specs, whatever I wanted he did. I was very hesitant about the whole thing but man, what a great guy and so generous!!! I was content with a stripped down simple as possible patio model but he would have none of that!!
It works just fine all seasons just the way it is. Sure it takes a little more wood to get it to temp in below freezing weather but I think it would anyway insulated fire box or not
After its warmed up it takes about the same amount of wood per cook as it does in the warm weather
here it is, in the one pic I am meeting his lovely wife Sharon, she met me 1/2 way with it