At least with the GMG, I've not cared for chicken skin that much. Yes the meat comes out moist and mildly smokey but it always seems a bit rubbery, even cooking at 350.
So I think I've found the solution for the leathery/rubbery skin. It's a combination of a few things I've heard/done over the years.
To get the skin to crisp up/be edible, you need to dehydrate it and render it (duh!) but doing that correctly is the trick. Now when I was oven cooking pork belly (skin on) in the UK, everyone always said to rub the skin with salt so it will crisp up properly (OMG pork belly cracklin' is the best) so that's what I always did and ended up with nice crispy skin. Oil is the second trick to get things to render quickly.
So, on to the tricks.
1. Pre-season your yardbird about 30 minutes before you cook it. If your rub has salt, you're good. If it doesn't, you may want to consider salting, then applying the rub. If you can't tolerate salt ¯\_(ツ)_/¯
2. Oil yer bird. I saw a recipe that recommended buttering the chicken, then applying rub. What a giant pain in the butt that was, messy and not very effective. I put the rub on, they spray it down with olive oil and LET IT SIT. This is part of the 30 min rest thing. The spices will absorb the oil and then they won't burn, and the oil will naturally spread itself out into a nice even coating. The big thing here is that the oil helps with heat transfer to the skin to render it. It also helps prevent the skin from drying out. Don't leave this step out.
3. Bird goes on the pellet smoker
skin side down first. Cook for 30 mins before flipping. This starts rendering the skin, since heat mainly comes from the bottom up on a pellet smoker, hence putting it skin side down. I cook at 275°. You can go higher, but I probably wouldn't exceed 300°, but feel free to experiment. Once you flip, you've probably got 15 mins until it's done.
I've been doing chicken this way for a while and have had good success. Haven't tested it with a whole bird, obviously hard to put that skin side down unless spatchcocked.