I grew up in Central Texas. We always kept the outside covered in a very light coat of oil. At the end of the hunting season, we cleaned everything we'd used that year and left a light coat inside. Like Afterum said, about every 6 months or so, we'd go back and run a patch through the barrel then re-apply a light coat. Seems to keep things in good working order.
You should remember to run a patch through them prior to shooting them the next time just to remove any oil/debris/dust the oil might have picked up in the interim.