Combine water, salt, and shrimp and crab boil in a large bowl; stir well to blend seasonings. Rinse fish thoroughly in cold water; place in brine mixture. Cover; refrigerate 30 minutes, stirring occasionally.
Prepare charcoal fire in smoker; let burn 10 to 15 minutes. Drain water from hickory chips to fill water pan half full. Sprinkle hickory chips over gray-white coals. Place water pan in smoker. Heavily grease wire food rack; place on lowest shelf in smoker.
Remove fish from brine; rinse thoroughly in cold water, and pat dry. Arrange fish on food rack; cover smoker with lid, and open vent slightly to keep smoke and air circulating. Smoke fish 1 1/2 hours or until fish flakes easily when tested with a fork and is golden brown. Transfer fish to a serving platter, and serve.