What is your plan for a fire?
It looks like you could make it work with a charcoal basket (uds style) and maybe use one of the lower shelves for a diffuser plate to even out the heat.
Then the rest of the shelves could just be a piece of expanded between the sides of the cabinet.
I have never messed with the propane side of things but I would guess to say it wouldn't be much different then the basket route. The diffuser plate would probably still be the same.
The stack, I would think wouldn't have to be any larger then 3" max. That is unless you are trying to make it where the stack will exit the box down low. But then you have to make it like a reverse flow and get the smoke to the top and it flows back down and out.
Remember you don't want to control your heat from the stack, you want to do that from the vent holes for the fire.
I think I would use 1 of these, and about 2' of 2" emt for a stack. I know its galvanized but if you get the top hot enough to cause a problem you arnt going to eating that food anyways.
You could probably use a pipe nipple and the lock ring off these fittings for the air intake for the fire. I could be wrong but I think HF has 2" ball valves for like 10 bucks. These are the brass ones or home depot has pvc valves for about that same price. You can try this like a uds also, one thread with a cap and one with a valve.
I can see this build working out very nice, with not alot of expense.
You might save a little money by locating felt like the BGE uses for its lid, and use that to seal your door instead of the fireplace rope.
If you get somewhat of a plan and your materials my plasma will make pretty short work of the vent hole circles and cutting up the expanded grate. I would be glad to help ya out if needed.
One last thing is, maybe check out Asners scrap metal on James st in KCK. He has alot of crazy stuff like grate material, some of it even stainless. I know scrap is high right now but its still probably cheaper then new.
