Put the salmon in a large plastic container skin side down and cover completely with rock salt. Spread brown sugar liberally over the salt. Drizzle soy sauce over the brown sugar. Let sit for 1 hour, spooning liquid over the fish several times while sitting. Rinse off the fish with cold water. Drizzle small amount of maple syrup on each piece of fish and spread around with fingers. Sift a little brown sugar evenly over fish and place in smoker.
Smoked the salmon at 175 degrees for an 3 to 4 hrs. Smoking time depends on the thickness of the pieces and how you prefer your smoked salmon (soft ,medium, hard or jerky). I usually start poking it with my finger after three of four hours, and when it starts to firm up, it’s done as far as I’m concerned. Thick pieces of a big king salmon can take 8 to 10 hours.