MG,
Metal is the same all the way around...10 Gauge CR steel that is .134" thick. I don't have to choose where to insulate, because the entire thing is insulated...if there isn't a cross member, there is insulation. I have found that it makes such a difference, as weather has no impact whatsoever. My verticals are really efficient, this last weekend going for over 12 hours at 250° with a little over 1 1/2 chimneys of charcoal and a couple fist sized pieces of apple chunks. Because I am using a heavy gauge metal, the exterior does get warm due to the heat sink effect of the metal, but that is it, just warm. You can set your beer coozie on top of my smoker with little fear of melting the coozie, or worse yet making your beer warm!
Sunday I had a bunch of neighbors over and help me rotate the smoker so I could work on the back. I cut the outer shell to size, and marked it for some black pipe pass throughs. Here I am marking out the placement.
Got the holes drilled through both skins, making sure that they were perpindicular to the shell.
Fitting the pipe to make sure all is good!