Yeah, I checked out the link and located the ceramic fiber stuff yesterdayday when I discovered to email you sent me. The 1/2" looked like the best value:
93315K42 Ceramic Fiber Insulation Blanket 6 Lbs/cu ft Density, 24" 25' X 1/2" Thk, White $ 38.50 Each
This stuff should probably be used like a temporary blanket to be used when weather conditions dictate and not permanently iinstalled. I would simply cut strips about 6" longer than necessary for all the sides and hold it down from the top of Bandera smoke chamber with bricks or maybe an angle iron 3-sided frame. Tape the 2 sides and back but not the front (obviously). Mcmasters also had some tape that should work well for this (4057K7 Ceramic Fiber Insulation Tape 3" X 25' X 1/32" Thk $ 35.93 Each ). The front piece would be a drape so you can get stuff in & out.
Keep us posted if you do this, okay? I just might want to make you an offer on any surplus material.
Mark (STL)