Keeping the tools at a more constant temperature would help. If the tools are much cooler than the air around them, water will condense on them. Every day the air warms more quickly than a chunk of steel, so they get slightly wet most cold days. A closet for your tool box with a light bulb or gun safe dehumidifier in it would help a lot.
Camphor works, but depending on the scale of your tool box it might be a pain. The desiccant packets don't last long open to the air because they are really designed for sealed spaces and they fill up quickly with moisture from the air.
My long-term plan is a "closet" for my unheated shop, but my wife's short-term plans keep getting in the way.