In a small bowl mix all the spices together (even the pkg of spices with the corned beef) until combined.
Rinse the corned beef and pat dry with paper towels.
Layout two pieces of aluminum foil slightly overlapping. Place the corned beef in the center of the foil. Coat the corned beef with the spice mixture, and drizzle the liquid smoke over the top is using. Flip so the fat cap is at the top and wrap tightly with the foil.
Roll up four large foil balls and place them in the bottom of the slow cooker. (Or you can use a rack if your slow cooker has one) Place the wrapped corned beef on top of the foil balls.
Cook on low for 9-10 hours. Remove beef and place on a baking sheet, cool, and then place in the refrigerator for 3-4 hours. Reserve the juices from the slow cooker, and from inside the foil.
Preheat the broiler to high and set the rack about 6 inches from the heat. Remove the beef from the foil and place it directly on the baking sheet. Broil 3-4 minutes, watch closely so it doesn't burn. This is to set the crust; you're not trying to heat it all the way through. It slices much better when it's cold.
Slice thinly and serve with reserved juices.
To Assemble the Sandwich
Toast your bread or sliced rolls. Place your meat on one half of the bread and then cheese place it under the broiler for 2-3 minutes or until the cheese is melted. Place remaining bread on top and serve.
Notes
If you're concerned about corned beef being too salty, you can soak the corned beef in cold water for 4 hours, prior to cooking.If your corned beef is on the smaller side, like 3-4 pounds cook for 7-8 hours.Juices will collect in the foil and some in the bottom of the slow cooker. Save it all for later.You can add a little water to the reserved juices if you find it too salty.