adlee wow I can tell you have really been thinking about this. Thats pretty much the same process I went through.
Ok I will email pics.
The hot plate is mounted from under the fridge ( in the compressor compartment) ONLY the element is actually in the fridge (smoking compartment) therefore I can go under (where the compressor was) and adjust the heat. I divided the compartment off in two sections. One side has the hot plate control the other is the entry point for the smoke generator. I cut another hole in the bottom of the fridge compartment for the smoke to enter the fridge. Therefore the hot plate is indeed above the generator. Because I divided the bottom compartment in two I can open the one side to adjust the heat and not open the fridge or open the side where the generator is busy pumping out smoke. If I do have a problem with the generator I can open up that side and not effect the heat. I bought the grates or racks at a place in Canada like Cabellas. They are a perfect 24 wide by 12.5 deep. They are used for placing above a camp fire, I just cut the legs off of them. They were cheap for nickle coated stainless, less than $10.00 each. I will take some good pics in the daylight Tuesday and email them to you. Please remember this is still a work in progress. Although very functional it needs a make over to really make it something I wouldn't mind showing off.
I had no problem with the coupler as mine is also very thick, BUT the bottom compartment is only single thick not double metal with insulation in between? I Actually lined the bottom comparment with 1 inch ply wood (thats how I divided the sections) piece of cake, no heat as the the element is closed off in the the upper sections. This will be easier to understand when you see the pics. Anyway it works AWESOME and I do not have some of the problems I read about in the forum (not enough heat, opening the door and loosing heat, too long to get up to heat etc.) BOught the thermostat at an appliance parts place the j coupler (heat probe) came with it. Explain to them there what you want do and they will likely tell you exactly how to.
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I'd walk a thousand miles to smoke a "Camel"