Can I store clothes and mattresses in a container?

What actually happens when a mattress leans on steel

Picture a mattress standing on its side, leaned flat against the container wall to save floor space, which is exactly how people naturally pack a truck or a box. Overnight, the steel outside cools, the inside face of that same wall drops with it, and any humid air inside the container condenses right where the mattress is touching.

By morning there's a damp patch on the fabric where it met the wall, even though nothing leaked in from outside and the container itself is completely dry and sealed. That's not a flaw in the box. It's what any cold, sealed metal surface does to warm, humid air, and fabric sitting against it is the first thing that shows it.

The rule that follows: air gap and elevation

Once you see why it happens, the fix is obvious: don't let fabric touch the steel, and don't let it touch the floor either. A couple of inches of air between a mattress and the wall is usually enough for that spot to stay as dry as the middle of the container.

• Stand mattresses a few inches off the wall, not flush against it
• Pallets or a floor covering under mattresses and clothing bags, never bare steel floor
• Vacuum bags or sealed totes for clothing staying more than a few weeks
• A vent so the air inside has somewhere to go besides the ceiling and walls

A move is different from a season in storage

If a mattress and a few bags of clothes are only in the container for the two or three weeks around a move, the air gap and pallets are really all you need. Moisture takes time to build up, and a short stay doesn't give it much.

Storing off-season clothing or a spare mattress for months at a time is a different job. That's when the vent earns its keep. It's an easy add whether you're buying or renting, and once air can move through the space, condensation mostly stops forming on the walls in the first place.