When storing boxes, the sides of the cardboard boxes must never touch the concrete walls or be placed on the bare concrete floor.

You must leave a space between the box and wall or line the wall and floor with thick plastic.
Reason being, that if the cardboard touches the concrete it will attract and trap moisture which will damage the boxes and eventually the contents.

Everybody knows that our climate is very humid and even if the unit are ventilated the moisture in the air will condensate there where contact occurs.