Got the briquets today. First I fired up the 380 set at 225* and spent an hour observing the following with my ThermoPro in the center of the grate.
1. 20 minutes the Actual temp was 230* and ThermoPro was 308*. Then it slowly settled down to Actual temp of around 224-230, with ThermoPro temps from 217 to 250* plus/minus. No real stabilization at any time. I waited another 20 minutes (total time 80 minutes) and called it quits.
2. Then I let it cool completely until it was same as outside temp (around 56*)
3. Made a circle of briquets around the bottom as far away from fire pot as possible. And in addition placed a circle of bricks on the center of the diffuser plate where it is not perforated. So there was no impairment of air flow.
4. Turned on and set to 225* again. After 20 minutes the temps equalled each other for a while. Then came a pattern of ups and downs with the ThermoPro being as high as 50* above or 20* below the Actual measured temp, which varied from 218* to 235. Then I had a wide fluctuation of the Actual to as high as 280. While the ThermoPro got to 300* before I shut it down after 45 minutes.
5. Bottom Line: A waste of time. Briquets added no evidence of improved control or accuracy.
Conclusion: The unit is not capable of accurate low slow cooks on a consistent basis. I've seen nice results on a few items on You Tube, but have no info on what the true actual temps were. I credit those results to good chefs, who kept an eye on the process and adjusted as necessary.
I suspect as before that the problem resides with the controller, which suggests it is less sensitive to temp variations and is slower to respond than required. Thus it over and under shoots the mark most of the time. Also to some extent it is erratic all together in its response to low temps settings.
For myself I am satisfied that hot and sear is the best use for my 380. I also accept that the control problem may be unique to my unit, but do not wish to pursue this with RT. At high temps it is just fine and that was my original plan of use.