For 100% sure and certain protection the VCI paper and the special "hard" plastic bags, or the Zcorr bags with the VCI already in the bag is the way to go.
If you go with the VCI paper, DON'T use any ordinary plastic bags, they'll pass moisture and let the VCI vapor escape.
The VCI works fine for me. I bought some from S&W a few years ago and replaced the worn out and ripped ones in some of the boxes. I think I ordered 20 sheets last time.