In a large mixing bowl make a brine by combining 8 cups water and salt.
Soak trout in brine overnight in the refrigerator.
Rinse with water; pat dry with paper towels.
Lightly brush the trout skin and cavity with oil.
Stuff the cavity with tarragon.
Smoker directions: About 1 hour before cooking, soak 2 cups hickory chips in enough water to cover.
Arrange a full pan of coals in smoker and ignite.
When coals are hot, drain the hickory chips; sprinkle some over coals.
Fill water pan of smoker with water; set in place.
Place stuffed fish on grill over water pan.
Cover and cook for 1 to 1 1/4 hours or till done, replenishing coals, hickory chips, and water, if necessary, every 30 minutes.
Skin trout; remove head and tail.
Arrange on serving plate with lemon slices, lemon leaves, and radicchio, if desired.