I just did some a couple weeks ago for the first time and it turned out great. A guy on another board sent me this. I brined it all, smoked some, some plain, some w/ fresh jalapeno slices.

So here's my generic salmon brine, which a friend gave me. I vary it up a little now and then, but here's the base, nothing special:
1 GALLON OF WATER
1.5 CUPS OF SALT (NON-IODIZED of course)
1.5 CUPS BROWN SUGAR
1/3 CUP LEMON JUICE
1 TABLESPOON GARLIC POWDER
1 TABLESPOON ONION POWDER
1 TABLESPOON GROUND ALLSPICE
2 teaspoons BLACK PEPPER
I mix up 3-5 gallons depending on the meat volume I'm dealing with, and make it up on the stove to get things solubilized, then cool it in 5 gallon buckets for a good while so it's not warm when the meat goes in. I'll clean up the tuna loins, and then they go in the brine for 2 hrs 15 minutes (bit shorter if they've been frozen, bit longer if they're fresh). For reference so you can titrate to your dry brine duration, I usually soak previously-frozen chinook in this brine for 6 hrs. So maybe a little less than half of what you'd do to a salmon? Anyways. . .after the brine, rinse loins with cold water, and cut them to fit in jars, rack them on the smoker racks and let them sit overnight (give or take) to maybe let a pellicle form (or not, they turn out good going straight into the smoker too I've found). The last batch I actually did 2 pans alder chips on the big chiefs, which was good. One pan is good too. For reference I usually do 3 pans for salmon. My wife and I put up 6 big chiefs worth of these tuna loin MF'ers last fall during a can-a-thon, that we're still eating. That 2 pans seemed like reasonable smoke flavor to me at least, the 2 pans. While they're smoking I'll prep the jars. For jalapeno's I use the ghetto canned or jarred stuff at the store, so that I can use the liquid stock in there, that's what adds the flavor. Using the wide mouth half pint jars I add a teaspoon of jalapeno stock to each jar, a little handful of crosscut jalapeno's from the jar (almost doesn't matter how many, as I say, it's the stock that spices it up), and to some I throw in a cross cut of fresh ghost pepper to bring some heat. Habanero's work well for this too, although not as hot to me. I've heard carrots and other things you have laying around are good too. I throw in a teaspoon of olive oil too, but I'm not sure it's necessary. Then can like you usually would.

This is all a bunch of F'in work. Keep in mind I always like things way more complicated than they need to be, that's just me. But it's good, and when it's done you have enough to last a year (hopefully). My stash is getting thin, so I'm hoping this allegedly great tuna year has a couple more weeks on it, as I'm hoping to get my boat out over the bar the last weekend of Sep for a couple days of it. Hope you've had a good summer, and hope this is all useful,