Avoiding destructive corrosion is fairly straightforward. As already mentioned, just make sure it's clean to begin with and keep it dry. To preserve it without tarnish, it would need to be protected from gases (air) that can contain molecules that will tarnish. Vacuum-packing can minimize this. To eliminate it, I would suggest metal containers, nitrogen-flushed before sealing with nothing else inside. For practical purposes, eliminating darkening or tarnishing of the brass isn't necessary, but it can still be desireable.
There is not a good reason to use Water Displacement formula 40 if you can protect the item from water and water vapor using a physical barrier like a sealed bag or box. As mentioned already, paper boxes can cause tarnishing and corrosion. Not only are they likely to contain some moisture, but they also contain free sulphur and volatile sulphur-liberating compounds, and some amount of formaldehyde (as do all wood products). Formaldehyde breaks down to formic acid. So-called "acid-free" papers typically contain high levels of sulphur.
There's some evidence that bubble-wrap can have contaminants that will cause tarnishing probably because it can be coated with "saran," or Polyvinylidene chloride (to keep the air in the bubbles). I'd watch out for plastic-wrap also which has been made of the same stuff. At some point, food-grade wraps (other than for meat) were switched to polyethene because of the chlorine in the PVDC. The problem with polyethene is that it has a higher oxygen permeability (why it's not used for meat). Adhesive labels (stickers) are a major source of contamination within a small, sealed environment, so avoid using those (and take precautions if using any paper label).
