Hey DDS,
Sorry I haven't been paying attention to the Fridge builds section for a while. Your fridge looks a lot like mine (
http://www.smokingmeatforums.com/t/105764/heres-my-fridge-build-mid-build) I opted to go the super cheap route and use scavenged oven parts to produce/control the heat. I use chunks of wood on the element, like ECB, to produce smoke. But I do use an AMPS for cold smoking bacon and cheese.
Some of the pics from my post might help you but a couple of things I know now. closest shelf needs to be minimum 12"-18" away from element. I have a shelf bracket that is only like 3 inches from the element and I intended to use a water pan to help even heat, provide moisture, and catch drippings. Three inches is way too close and it basically zapped all my heat before it can heat the rest of the chamber.
I used the same 24ga steel I used for the door to cover that back hole. People tell you that you need to use stainless so it doesn't rust, well that's hogwash. If you season your smoker with some oil you'll never see rust. As for my shelves, I used angle iron brackets and expanded metal. I apparently have a pretty good hook up on steel tho, so it might be more difficult for you to find (cheap).
Note my smoke stack; straight piece of dryer vent $1.99 at the farm store. Cut 6 inches off the non-tapered end and inserted that into the hole I cut (hole saw) then cut 1" slits and folded back the egdges and screwed it down on both the inside and outside. Then the tapered end inserts into that snug as a glove. I did seal the inside then to keep it sealed up. I kept the piece of steel I cut out of fridge exterior and made a in-tube dampener.
One thing that Dave mentioned and I learned; condensation (especially us northerners) will form in the stack and drip back into smoker. I've since build a deflector that catches the condensation and sends it down the back of the smoker.
Airflow was an issue for my smoker but I solved it by installing a muffin fan ducted into the smoke chamber. I've got this setup on a separate switch and when I add wood I flip the switch on and get plenty of air moving then shut it off and it takes over on its own. When I'm cold smoking with the AMPS the fan is on the whole time, element is never on (obviously).
As you can see I used lava rock as a barrier between my element and the bottom of my fridge. Stole that from ECB as well.
I'm subscribed now so any other questions you have ask away and I'll try to get back to you ASAP. PID is a super nice setup, I just went the cheap route cause I had all the parts. I haven't taken any pictures lately so let me know if you would like some additional pics and I can snap a few.
Enjoy!!
-Josh