If the tools were used, I would put enough air tool oil in the air inlet that the tool starts blowing the oil out when running. This will displace any moisture trapped inside. It is messy, but will keep it clean and from binding up. Oil on the outside, then placed in a plastic bag works. We like a product called T9 or Boeshield. We used to sell it, but due to hazmat we choose not to ship it now. It is basically paraffin that is emulsified in mineral spirits. Spray or wipe it on, the mineral spirits will flash off and the paraffin protects the surface with a thin wax coating. It has preserved a milling machine of ours for years now. I know there are some similar products for aircraft corrosion protection, you might check with a local mechanic if you only need a rag full.