Thanks for this info. In the last month I did a whole turkey and yesterday did a load of boneless chicken breasts, and both took 2-3x as long as normal here in Denver (around 27* yesterday, and generally breezy/windy). The links posted early in this thread are both broken, and I sketched a wooden box type enclosure. However just decided to see how a welding blanket would work, so Harbor Freight with $7 shipping and 20% coupon and I ordered a 4x6 welding blanket and a mess of 1" metal spring clamps for $36 shipped to my door.
In the past I've used the roll type of alum faced bubble wrap stuff about 1' wide from Lowes which works good but melts if it touches the wsm, and I was afraid of the same with the water heater blanket. Put that stuff around the smoker and temp would go up 15* in a matter of minutes, it really helps to block the wind from the seams and the door of the wsm.