I originally built my own equipment for controlling the inlet-air dampers on a smoker (a Big Green Egg [BGE]). This worked really well, and was very consistent in the smoking temperatures it provided. I sometimes still use it today, but generally now just forgo that approach, as on low-wind days I find the BGE is close enough without the extra controls.
Sometime back, I became aware of Sous Vide cooking via the book 'Cooking for Geeks'. Given my BBQ background and slow smoking BBQ, I grasped this was the approach I first came across via Harold McGee's book 'On Food and Cooking'. This was too big to pass up now that I was retired!
So I gave it a try. Rather then buying any of the expensive commercial Sous Vide equipment, or even any of the other DIY less-expensive approaches, I adapted my thermocouple controller, which had built to control my BGE, to control a hotplate where I placed a large iron Dutch Oven (Lodge) and filled 3/4 with water. My first attempt was cooking 2.5# of Brisket. It worked out great! But the Dutch Oven was a little small for the larger Briskets, so another approach was needed, and it was sort of kludgey using my controller in the kitchen.
When my wife wasn't looking, I grabbed her electric 'Roaster Oven', a 20 quart beast that operates on 110 AC household electricity. My wife had lost confidence in this roaster when her Turkey came out way-under-cooked one Thanksgiving, but I hadn't been ready to throw the roaster out yet. Fortunately we had tested the temperature of the turkey with an internal probe and found it very low, so we moved the turkey to our main oven to finish.
For the Roaster Test, I filled the roaster 3/4 full with water, then inserted a remote sensing temperature probe (Taylor's Gourmet Stainless Steel Thermometer with Probe from Target) into the water. Setting the temperature to 150 dF as indicated on the dial of the Roaster, I waited patiently for the temperature to come up to 150 dF. It never did. I checked the temperature with the Taylor probe, and it was low, really low, around 100 or so instead of 150. That pretty much explained the turkey fiasco of a previous year! The printed temperatures on the roaster were way, way off! Using the Taylor, I spent the next day finding the proper dial position to obtain 100, 150, 200, 250, 300, 350 and 400 degree placements and marked those with a Sharpie perm pen.
I tested the markings for 2 days - they held consistent, so while the markings were way off, the Roaster's thermostat was capable of holding a temperature +/- 1 dF, which for me was more then adequate for doing slow cooking of Brisket.
So using my new markings along with the Taylor to monitor, I set a temperature of 142 dF for a new trial run of Brisket Sous Vide. I refilled the Roaster 3/4 full of water (about 4 gallons), and brought it up to temperature over a couple of hours to ensure it stayed there.
Meanwhile, I browned both sides of a 5# Brisket in an large iron skillet. It was too big to place into a single 1 Gallon Ziplock storage bag, so I sliced it into 2 equal portions, cutting with the grain, and inserted each half into a seperate Ziplock, then carefully submerged while leaving a vent for air to escape. This is important, as you don't want any air pockets to separate the Brisket from the surrounding water bath, as then it won't cook evenly. When the water level came up to the Ziplock opening, I sealed off the Ziplock, and let it sink to the bottom of the Roaster.
On one Bricket, I placed a whole bottle of A-1 brand meat marinade; on the other Brisket, I left it unchanged. Both were then closed off and placed into the water bath.
BTW - the Ziplock company has stated (per Cooking for Geeks) that their bags are good up to 170 dF, although they don't recommend using them.
That was yesterday evening. I've checked every couple of hours or so, and the temperature is holding constant between 141 and 143 dF.
Tomorrow night will be the test! That will be 48 hours at ~142 dF Brisket!