I agree with the earlier comment that it is important to wipe tools down before putting them away, and not just the greasy tools, either. I have wrenches, sockets, etc (let's call them 'automotive tools') in steel tool boxes out in the garage which is unheated. Temperature and humidity fluctuate violently at times, but none of the tools ever rust. No packets of silica gel either. I just make sure that any tool taken from the box gets wiped down after use and as it is being put away.
I suspect that the humidity in the tool box only really changes when the drawers are opened. When they are closed there is nothing to promote the flow of air, thus temperature and humidity changes are very slow inside the drawers. When those changes occur slowly enough, moisture never condenses on the items inside the drawers. As already mentioned, consistent temperature and humidity are a big help in preventing rust on tools and machines.