I finished my smoker and figured I would post a picture. I spent a lot of time lurking on the forum getting ideas from past posts, thanks to all. This place is a really great source for information
The design is a double walled smoker. I was able to source a new, sandblasted bare 55 gallon drum (we call them 45's up here because of the imperial vs U.S. barrel volumes). I then placed the 55gal inside a new 85gal "salvage" drum (sometimes called over-pack or containment drums). I used 1/4" metal rod for spacer to float the 55gal drum inside the 85gal. I ran 4, 3/4" pipes through the 85gal drum and into the 55gal. I sealed up around the openings around the 85gal drum with RTV silicone (I wasn't too worried about choice of sealant as there is no communication with the inner cooking drum).
This keeps a "dead" air space between the two barrels in an attempt to insulate for winter use. I want to be able to run this in winter when free time is at a maximum, and these Canadian (Saskatchewan) winters can get down to -40F (not factoring in wind chill). I ran it yesterday for about 6 hours on ribs, and it worked really good. I would say it used about 3 lbs or lump charcoal, and seemed to settle into 230F with 2 valves closed and 2 about 1/2 open. The outer barrel hardly gets warm with it running.
All in all, it seems to work good with no complaints yet. Those salvage drums are about $200 new around here (vs $50 for a new 55gal), but they seem to have nearly twice the wall thickness as the smaller drums.