I use a dry brine recipe that I have been using for more than 15 years. What I like about it is it's simple, inexpensive, quick and has always tasted great!
I always freeze my salmon for 3 to 4 days before smoking. Before freezing I cut the fillets into about 1.5 inch strips. (This give a lot of surface area for flavor to be added) After defrosting them slowly in the fridge, layer them in a glass or plastic pan skin side down. (do not use a metal pan!) Sprinkle course kosher salt and brown or demera sugar on each fillet strip. (About 1/8 to 1/4 inch thick) Use salt and sugar on a ratio of 2/3 salt and 1/3 sugar. Put another layer of salmon on top and coat with salt and sugar. Keep layering until pan is full or you run out of salmon.
Put the pan in the refrigerator or a cool place and leave it sit for 3 to 4 hours. If you are smoking spring salmon you may want to leave it for up to 5 hours because of the thickness. You'll be amazed at how much liquid is drawn out of the salmon in such a short period of time.
Rinse each piece of salmon under running water and pat dry. I layer them on the counter using paper towel between the layers. Place the dried fillets, skin side down on the lightly oiled smoker grate. Then I sprinkle them with fresh ground pepper and dried chili flakes. You could use all sorts of coatings at this stage including maple syrup or a honey/water mixture, etc. My family prefers the basic salty, sweet, savory taste with a bit of heat from the chili flakes.
The next step is very important! The fillets must be dried to the stage of being sticky dry to touch and having a shiny look to them. You can use a fan or put the grates into the fridge over night. (I use an old fridge to do this) This dry sticky coating is called pellicle and is necessary for the smoke to adhere to and in order to seal in the fats that will otherwise seep to the surface of the fish while in the smoker.
I have a bradley and I smoke with 7-8 pucks (about 2-3 hours) at 100 degrees. Then I slowly bring the temperature up to 150 degrees over the space of 3- 5 hours. I like the salmon to be flakey and moist, not too dried out. What we don't eat right away I vacuum pack and freeze.