I have read many, many emails and net comments about my Masterbuilt 30" smoker that I was afraid I would not be able to fast smoke, slow smoke, or even cook on it when it was below 30 degrees F. So I went rube goldberg with a insulating idea. I used space blankets. The plastic blankets have a melting point of 345 F and my smoker never gets that hot. I used aluminized tape to tape each side individually with a heat reflective blanket and left the smoke roound door open and the vent open. I have about 80 percent of the smoker "reflecting heat back to the unit" so to speak. I started the smoker at 12:15 today and it got to 250 in 15 minutes. The outside temperature is 18F with a slight wind on my back screened in porch.
I have a cold smoke attachment so I filled it with chips and put in a 5 lb. chicken, and a rack of Louisana style pork ribs. It is now 4:45 pm and the ribs are looking great and the chicken is up to about 155 internal temp. (I checked it with a separate meat thermometer).
The MBS heat probe is not accurate as far as I can figure out. Master build internal says 166 but I do not believe it. Perhaps I did not have to "insulate" my smoker but it is performing beautifully at 18F and is mainting temperature just fine. Love it so far. I am using beer in the water tray and apple and cherry wood chips.