I use an electric smoker, with a water bowl under the two grills. Soak your chips for at least an hour, more won't hurt. I use either hickory or mesquite.
I don't brine I use a dry rub, but I coat the fish in some olive oil then start sprinkling on the herbs and spices.
Old Bay
Cracked Black Pepper-lots
Smoked Paprika
Cumin
Sea Salt
Celery Salt or seeds
Chili Powder
Oil all sides then season heavily all sides. Let stand about an hour.
Smoke on Medium, and depending upon the size of the chunks or fillets 2-6 hours (the tuna in the pic went about 6 hours, thin fillets about 2 hours)
I replace the soaked wood chips when it stops smoking
I let cool completely then vaccum pack the individual chunks and freeze. I use it as is, or make tuna salad, or dip.
Reminds me, need to do another batch.