In a bowl, mix together salt, sugar, brown sugar, and peppercorns. Set aside.
Spread extra-wide aluminum foil a little longer than the length of the fish and top with an equally long layer of plastic wrap.
Sprinkle 1/3 of the rub onto the plastic. Lay 1 side of the fish skin down onto the rub. Sprinkle 1/3 of the rub onto the flesh of the salmon. Place second side of salmon, flesh-side down, onto the first side. Use the remaining rub to cover the skin on the top piece. Fold plastic over to cover, then close edges of foil together and crimp tightly around the fish.
Place wrapped fish onto a plank or sheet pan and top with another plank or pan. Weigh down with a heavy phone book or a brick or two and refrigerate for 12 hours. Flip the fish over and refrigerate another 12 hours. Some juice will leak out during the process, so make sure there's a place for the runoff to gather.
Unwrap fish and rinse off the cure with cold water. Pat salmon with paper towels, then place in a cool, dry place (not the refrigerator) until the surface of the fish is dry and matte-like, 1 to 3 hours depending on humidity. A fan may be used to speed the process.
Heat your smoker to 150ºF.
Place the sides of fish on the rack in the smoker over smoldering hardwood chips. Place a probe thermometer into the thickest part of one of the sides, and set the alarm to 150ºF.
Maintain the temperature inside the smoker between 150 and 160ºF. Smoke until the fish reaches its temperature, replacing the chips as needed. Serve immediately or cool to room temperature, wrap tightly, and refrigerate for up to 3 days.