Polish to Protect
Storage units -- even heated or cooled ones -- aren't always the ideal temperature for wooden furniture. Wood that's stored in unstable temperature conditions, hot during the day and cold at night, can crack, swell or shrink, causing glued joints to loosen. A coat of furniture polish can help seal wood, keeping furniture from becoming dried out due to poor temperature control while it's in storage. If you're storing valuable antiques or any wood object for an extended period, months or years, paste wax offers a more protective sealant.
Wrap It Right
Covering wood furniture protects it from scratches and fading from any light source. Wood wrapped with plastic can sweat, causing it to swell or rot, especially if the storage area is not climate-controlled. If the wood furniture has leather or fabric parts, such as chair seats, plastic covers can cause these to become moldy. Old bed sheets or soft blankets don't trap moisture, making them ideal furniture covers for storage.
Put Down Plastic
Often, storage spaces have concrete flooring. Moisture leaches from concrete, and can cause wood to swell or rot. Before placing wood furniture on concrete, lay plastic or a dropcloth on the floor to avoid the wood wicking the moisture from the concrete. Plastic sheeting or tarps act as a barrier between the floor and wood, keeping wood furniture safer and drier than without them.
Disassemble to Divert Damage
If you're storing wood tables or chairs with removable legs, take them apart. Not only does this make them more compact, so that they take up less room, but it also makes them easier to wrap than with the legs attached. And, this way, you won't be tempted to set other objects, such as boxes, on or under them, making them susceptible to scratches or dings. Store any removed bolts or screws in plastic bags, and tape each bag under its furniture piece and label it so that they don't become separated.
Build a Base
When possible, store your wooden furniture above the floor. Being raised, even slightly, protects it from flooding or leached moisture. Lay planks and plywood or wooden blocks, to act as a support or a subfloor to give your furniture a protective base or platform on which to wait out the storage period safely.