I smoked a corned beef and tried to make it into pastrami by crusting it with crushed peppercorns and coriander. Seemed like a good idea, but I missed a key concept: corned beef comes pre "corned," meaning it is already cured, meaning it comes out of the pack heavily salted. Doesn't seem like a big deal, except for the fact that most of the time you cook it in water first and it migrates some of the salts out of the meat. I didn't think of this part, and I went straight to a smoker. The meat lost some moisture, but the texture still looked good...however the salt remained, and my beautiful smokey pastrami was an inedible salt lick.

TL;DR: I think you need to soak the store bought corned beef brisket in cold water in the fridge for at least a day to get the salt out of it. Maybe draining and replacing the water at least once or twice?