Recently purchased this as a trial, and have only used it for three days. Materials: ABS, stainless steel Dimensions: Approximately 33 cm (height) x 39 cm (width) x 33 cm (depth) The bar on top of the rear box is metal. Backrest cushion is unused. The items included are the rear box, mounting base, hardware, two keys, and the instruction manual. It's large enough to hold a helmet and rain gear. (These are not included.) I didn't experience any rain getting inside. It costs about 17,000 yen when purchased new. Currently stored in a dark place after removal.