Step 1: Wash the fish well and cut it into 3-inch chunks.
Step 2: Make the brine: Combine the 1 quart of water and salt in a large nonreactive mixing bowl and whisk until the salt crystals dissolve. Add the ice water and let cool to room temperature. Add the fish. Brine, covered, in the refrigerator for 8 to 10 hours (or overnight), stirring a few times so the fish brines evenly.
Step 3: The next day, make the seasoning. Combine the vinegar, paprika, pepper, and garlic powder in a mixing bowl and whisk to mix. Whisk in the oil.
Step 4: Rinse the brined wahoo in a colander and drain well. Stir it into the seasoning mixture. Let marinate for 20 minutes, then drain well again in a colander.
Step 5: Set up your smoker following the manufacturer’s instructions and preheat to 200 degrees. Add the wood as directed by the manufacturer. Arrange the wahoo on the smoker racks (lightly oil them first) and smoke until fully cooked, 1-1/2 to 2 hours. When done, the fish will have a tan patina of smoke and will break into clean flakes when pressed. (You’re looking for an internal temperature of 140 degrees.)
Step 6: Transfer the smoked wahoo to a wire rack to cool to room temperature, then refrigerate until serving. It will keep for at least 3 days in the refrigerator.