I'm curious as well.
The smokers are not really made to work at low temperatures below about 200. To get the lower temps you need to install a needle valve. Check out my post at http://www.smokingmeatforums.com/t/128297/needle-valve-mod-using-bayou-classic-regulator#post_867931 for one of the needle valves. They are very easy to install.
So... not to beat the dead horse, but hows it working out still? At what temps do you regularly run the smoker? What is the highest you have run it since you've added the insulation? Thanks!
I am consistently running from 225 to 275. I have done turkeys and such at over 300. The insulation is still doing great. It has really been a great thing for these winter months! I have not had any problem with the insulation.
I have the same set up and have for a few years. Easy to put together and just gets jammed in a corner when no needed. The product give s a temp at 180deg. THis is when you will begin to have off gassing fro the plastic, but may be much lower than ignition. I find it to be an acceptable level of risk especially since it will be on the outside of the smoker. On most models, the main air intake is at the bottom, which I did not insulate. Really not different than microwaving your food i a plastic bag if that calms some fears. After a few higher temp cooks, the material stiffened a bit, but overall performance really wasn't impacted. I'm going to use it tomorrow again during a -9deg day....should be fun.
I would recommend this if you don't have the cash to weld a second wall on your upright and fill with rockwool. If I'm going to all that trouble, I'm just getting a better smoker.
I insulated a different kind of smoker three years ago with excellent results, after some trial and error. I have used high temperature insulation in petroleum refineries and other industrial areas,but I could not find a way to get some without buying a truckload or so. It is often fiberglass insulation, so I tried regular Johns-Manville 2 1/2 inch house fiberglass insulation which is pretty good for temperature resistance. It is the binders and coverings that melt.
I wrapped my cheap offset smoker (a small New Braunfels of several years ago before they were bought by Char Broil) and fired it up with charcoal. What an amazing improvement. The temperature variations were way less and the charcoal lasted about three times longer. Propane would be the same. Sure the coverings melted on the inside. The insulation was fine, even over the firebox.
I got more insulation (left over from my house actually). I cleaned off the smoker and sprayed it all over with high temperature paint to avoid any rusting under the insulation. I wrapped the insulation around the body. This got covered by a sheet of duct sheeting that I cut to shape and screwed into place to hold the insulation. I left the ends open to avoid any moisture accumulation to evaporate. This prevents rusting rusting under the insulation which can be a problem.
This setup has worked and stood up very well for nearly three years now. It does take a long time to cool off if it gets too hot so I raise the temperature carefully.
Bottom line is that insulation really works, it likes to have a covering of sheet metal to keep rain off and protect it. Pay attention to rusting under the insulation, and use this high temperature grill paint from ACE or other places.