Abstract: A weatherproof system for cargo containers has therein an outwardly open lengthwise channel or groove formed in each of two opposing side edges of a floor panel 1, and the lower portion of one of four side panels is disposed immediately outward of the groove in such a way that a water trapping chamber is defined between the lengthwise groove and the lower portion of the side panel. The bottom surface of the water trapping chamber thus defined is in substantially coplanar relationship with an adjacent seat surface which supports thereon the bottom edge of each of the side panels, and the upper wall of the water trapping chamber is extended outwardly so as to define a water drip or barrier means. Therefore, rain or sea water flowing along the intersurface between the floor panel and each of the side panels is entrapped in the water trapping chamber and consequently prevented from further flowing into the interior of the container.