When looking to get a small grill for camping out of our 5th wheel, I purchased a GMG DC but experienced major temperature fluctuations as well as large gaps around the lid, so I sold it to a friend who has had good success with it. Yes, I did explain to him my complaints before I sold it. I had put a gasket sealer around the lid opening, but then pits are vented so did it really matter that there was a gap. In hind site, I was probably too focused on the fluctuations instead of just using it. Also, It was just a bit small for my liking.
I now have a Traeger Junior with the folding legs which has served me well. It doesn't have a stack, but vent holes in the back. Which again supports my changed thinking about the gaps in the lid on the GMG DC. Did it really matter?
If I were going to buy a new portable unit today, I think I would get the Rec Tec RT-340