A truck box includes front and rear corner brackets and an inner side panel having a first end fixed to the front corner bracket and a second end fixed to the rear corner bracket. A rail longitudinally extends substantially the entire length of the inner side panel and has a first end fixed to the front corner bracket and a second end fixed to the rear corner bracket. The rail has a center portion fixed to the inner side panel. The first and second ends of the rail are transversely offset and spaced apart from the inner side panel.