Like the Timberline and Ironwood grills, the Silverton does not have a smokestack. Traeger does not sell custom insulation blankets for these grills.
I believe the bottom and sides of the Silverton have two layers of metal. Some people have stuffed insulation between the two layers, but you have to be careful that the insulation does not get soaked with grease. The lid of the grill is only a single layer of metal. If you do plan to do cooks with temperatures below 0 F, you might want to purchase a welding blanket to lay over the grill to provide additional insulation. Just make sure that the blanket does not block the exhaust vents on the back of the grill.
Also insure that the grill is sheltered from the wind as that will make the heat loss even greater.,