Abstract: A collapsible container system for use on the bed of a truck including a flexible, water resistant, fabric bag assembly having a sealable opening in connection with a storage chamber for storing articles to be transported. The bottom of the bag assembly is coated or otherwise treated to be waterproof so that standing water is prevented from soaking through the water resistant fabric. The container system also includes a pair of rigid braces that are securable to the interior surface of two opposed sidewalls of the bag assembly. Each of the rigid braces extends to the corners of its respective opposed sidewall. The exterior surface of each of the opposed sidewalls is provided with a mechanism for securing the end of at least one and preferably two or more securing cords. The other end of each of the securing cords is provided with a mechanism for attachment to the body of the truck.