Mix together the Water (1 gallon), Salt (1 cup), and Granulated Sugar (1 cup) until dissolved in a large pot or another container.
Add the Whole Chicken (1) and enough water to cover, then place in the refrigerator for 4 hours.
Rinse the chicken and pat dry. Allow to thaw if needed.
Combine the Salt (2 tablespoon), Brown Sugar (2 tablespoon), Garlic Powder (2 tablespoon), Ground Black Pepper (1 tablespoon), Paprika (1 tablespoon), and Fresh Rosemary (1 teaspoon) in a bowl.
Rub the entire chicken with Olive Oil (1 splash) and sprinkle liberally with the spice rub mixture.
Place the chicken in a cast iron skillet and smoke between 225 and 250 degrees F for 3.5 to 4 hours, until breast meat reaches 165 degrees F.
Remove to a platter, tent with foil, and allow to rest for at least 20 minutes.