The "Golden Rod" is the most effective and trouble free, but you must keep it plugged in. In any case, wiping down guns to be stored with something like Rig gun grease is a good idea.
I have a 'golden rod' and two boxes of desiccant which can be recharged by putting them in the oven every 4-6 months. Take no chances! The rod only makes it warm thus less humidity but the boxes of silicate absorb what is there.