Mix salt and brown sugar to create the dry brine. Place fillets skin side down on a rimmed sheet pan and cover with a thick layer of the mixture. Cover pan with foil and refrigerate for at least 2 hours. Longer is better (4+ hours), but don't refrigerate overnight, that's too much.
Rinse the fillets in the sink. Pat dry with paper towels and place back in pan, on a wire rack. Set on counter with a fan blowing on them until a pellicle forms, around 2 hours. The pellicle is ready when the surface is shiny and dry/tacky.
Turn on smoker at lowest setting (150 F).
Smoke to an internal temperature of around 130 F (around a 1.5 hours, 2.5 hours if cold/windy). That should minimize the amount of white albumin oozing out.
