Preheat your smoker to 225°F and allow it to stabilize for at least 15 minutes.

Soak wood chips in water for 30 minutes if using a charcoal or offset smoker.

Pat the pork loin dry, trim excess fat, and score the fat cap in a crosshatch pattern.

Combine brown sugar, paprika, kosher salt, black pepper, garlic powder, onion powder, and cayenne in a bowl until evenly mixed.

Rub the pork loin generously with the dry rub, pressing to adhere, and let rest at room temperature for 10 to 15 minutes.

Place the pork loin fat side up on the smoker grate away from direct heat and insert an instant-read thermometer into the thickest part; close the lid.

Smoke undisturbed at 225°F for 90 minutes, adding soaked wood chunks after 30 minutes and maintaining a smoker temperature of 220–230°F.

When the internal temperature reaches 130°F, wrap the pork tightly in butcher paper or foil and continue smoking at 225°F until it reaches 145°F, about another 45 to 60 minutes.

Remove the pork loin, rest wrapped for 10 minutes, then unwrap and rest an additional 5 minutes before slicing against the grain.