Here are some photos that might be of help in sealing up the interior to prevent smoke and/or moisture from entering between the inner and outer walls. RTV hi temp silicon sealant is used in applications like this.
Got everything siliconed up over the past couple evenings. Did the crossover tube to fan in two different stages for ease of alignment. I don’t think we’ll have leak issues anymore. Once the back was off my smoker I could see a little leakage in those spots. I put a nice fat bead of silicone on all flats. The crossover tube was a little tricky but I sealed the outlet on duct work to back of smoker first, then generously applied silicone to inside of pipe and to outside of outlet on duct. It should be good. I definitely hope I don’t have to take apart again with all that silicone. Should have taken pics but was working alone and hands were a bit messy.