My barrels, whether in an infrequently used gun that's essentially stored or a barrel awaiting a project get an annual go-over. 1st, WD-40 followed by dry flannel patches to remove the stuff. 2nd, a flannel patch soaked with camellia oil (if it's good enough for the Samurai...). The wet patch gets used to apply a light film to the outside. 3rd, store in Sack-Ups--silicone treated fabric gun bags. 4th, store in a wood gun cabinet that's in a dry, insulated, heated attic.
It's always worked for me here in Wet-stern Washington. You'll get other techniques, I'll wager..........