Nothing to add to your setup except maybe some heat shielding down near the burners. I have managed to get a foil-lined tight-box set-up to 140F using heat lamps (for drying dirt samples)...but the burners you have seem that they would be easier to set/maintain a temperature. With the heat lamps we had on/off choices...no in-between.
I use a single burner countertop model and put a small cast iron skillet on it with a big chunk of wood. Plenty of smoke and heat. My brother sent me an old PID he bought from a cheesemaker supply company that just has an outlet on the back that I'm going to try next instead of having to fiddle with the control knob.