You are right and I have no argument with it. I'll add some comments though.
"Nice modding job there, but I would stay away from fiberglass entirely. Especially with open fiberglass, which your appears to be.
Every time you open the lids on chamber, or firebox, a tiny bit is going to float out... up, down and probably, into your food.
I'm sure it controls the heat, but I don't like little floating threads of glass in my food. It's almost as easy to ingest fiberglass without knowing it, as it is to inhale asbestos without knowing it. Once it is inside of you, it can cause serious problems, immediate or down the road awhile later."
1. The fiberglass does have a binder and is not totally loose. It is not real firm, either, and that is why I put a metal sheathing on it. This is the way I have insulated equipment in petroleum refineries and chemical plants.
2. This was a proof of concept idea. The concept does work real well. I welcome suggestions for a better implementation.
3. There is a general concern about moisture getting under any insulation and rusting the underlying metal. That is the reason for the open design - ventilation and drying of condensation. Condensation is a special problem when the smoker gets cold overnight and them a warm humid air mass moves in during the next day. I might have been too worried about moisture as it seems to stay dry here in Colorado at 5800 ft.. I don't leave it out uncovered though.
4. I liked the idea of a welding blanket or equal, but felt the thickness and insulating value was less than I wanted. The 2.5 inch blanket is better. Also, a blanket would need to be cut to fit and this would open loose edges to whatever filling it might have. A local BBQ shop has a Traeger with an insulating blanket that fits nicely and has the Traegar name on it. They use this unit for BBQ demonstrations for their in house classes and it shows a lot of use. I have never seen one for sale, but haven't looked since I don't have a Traegar.
5. I plan to insulate the smoke stack end this spring. I might cover the open ends at that time.
6. No good alternate materials showed up in a pretty extensive search of insulating materials here in the Denver area. There are some industrial insulations but you need to buy a huge quantity. Flexible insulation is a lot easier to work with than rigid.
The bottom line is that insulating a smoker offers real benefits in more even temperatures, much better temperature control with changes in the weather, and reduction in charcoal use and resulting ashes. Down sides can be increased corrosion inside the firebox due to higher wall temperature, and due to trapped moisture outside. High temperature grill paint seems to do a pretty good job.
Thanks for your comments. Please, everyone, forward your further suggestions.