Your Brine can Be as Simple as Salt and Brown Sugar
This is my go to recipe
2 quarts Apple juice/ Cider.
1/2 cup Salt ( I use pickling salt)
2 cups Brown sugar
1/2 cup soy sauce ( sashimi style its a lil bit sweeter)
4 Tbsp of chopped Garlic. ( More is always good)
2 tbsp lemon juice.
Mix Well and Soak fish for 48 hours.
The key after the brine is letting it air dry to get the tacky glaze look on the fish.
You can do this by leaving on the counter / having a small fan helps
or leaving in the fridge overnight.
Start the Smoker as Low as you can go. 100-125 to start up to 8 hours if you have time. Just remember to raise the smoker temp gradually .