Many deck box listings use the word waterproof, but most makers who explain it in detail describe their boxes as water resistant. Lifetime states plainly that its storage boxes are not waterproof. Water can get in through lid gaps, seams and vents in heavy rain, and condensation can form inside even when no rain gets in.

This guide covers where water gets in, how to set a box up to stay drier, and how to store cushions and gear so they do not turn musty. For picks, see Best Deck Boxes.

Where Water Gets In

  • Lid gaps and hinges, especially when rain is driven by wind.
  • Seams between snap-together panels.
  • Slatted sides on wood boxes, which are not designed to keep rain out.
  • Condensation, when warm, damp air inside cools overnight.

Set It Up Right

  • Place the box on level, firm ground so the lid seals evenly. A warped or twisted box leaves gaps.
  • Keep it off standing water. A few pavers under the base can help water drain away.
  • Where possible, put it under an overhang or roof.
  • Keep the lid closed and latched in bad weather.
  • Follow the maker's assembly steps exactly, since a panel that is not fully seated can leave a gap.

Store Things Dry

The most common cause of mildew in a deck box is putting cushions or floats away damp. Dry everything fully first, in sun and breeze. For cushions, see Can You Leave Outdoor Cushions Outside?

Store cushions on edge rather than in a tight stack so air can move. Breathable storage bags add a second layer of protection without trapping moisture. See Best Outdoor Cushion Storage Bags.

Check It Through the Season

Open the box after heavy rain and on dry, sunny days to let air in. Wipe out any water, and clean the interior with mild soap and water if you see mildew. Keep chemicals such as pool products in their sealed original containers.

Safety

Lock the lid if children are around, and do not let children play inside or climb into a storage box.

FAQ

Are resin deck boxes waterproof?

Most are water resistant. Some listings say waterproof, but heavy rain can still get in through gaps and seams.

Why is there water in my deck box?

Usually rain through the lid gap or seams, or condensation. Check that the box is level and the panels are fully seated.

Can I store cushions in a deck box all winter?

Yes, if they are completely dry and the box stays dry. Check inside from time to time.

The Bottom Line

Treat any deck box as water resistant, set it up level and off standing water, and store only dry items. Airing the box out now and then does more to prevent mildew than any single feature. See Best Deck Boxes and Best Metal Deck Boxes.