Wind is a big factor, but the insulation keeps the fuel use down. I've done comps at 35 degrees w/o any insulation, just more attention and fuel, but so easy to use insulation, so why not?
Man, that is one sweet set up. One question, do you have anything that vents smoke out of the shed? As for Fireproofing you might want to consider a layer of 5/8" drywall.This is what I put together for my WSM to get it out of the wind, I have it bolted to a turntable so I can get to all the vents for adjustment. I have vents at the top that I open for relief and I crack the door during a smoke for draft.
I like it as well...thought of something similar for the drum. WSM Smoking Jacket. I'd get one if i had a WSM....18" Is 99 and the 22 inch is 135 i believe. It serves as a cover also.Man, that is one sweet set up. One question, do you have anything that vents smoke out of the shed? As for Fireproofing you might want to consider a layer of 5/8" drywall.