I've got an 18' flat bed trailer, but all my chains, binders, straps and misc have been setting in the back of my truck for years. Every box I've seen is either far too big to fit like mine, or would have to take up bed space, so I set in on building my own.
Off to the scrap yard, and I picked up a couple pieces of sheet, got some 1" strap, and started in. This is what I ended up with.
Inside, welded front to back near the top, is a 3/8" rod to hang chain hooks from so I can grab chain without having to wade through a pile of chain. On the right is a tray at the level of the trailer frame to put motorcycle straps. Mounted at the back is the battery for the trailer brakes, which is sealed and drained through the bottom (mounting bolts lock the box to the trailer). The bottom of the box is protected with spray on bed liner. The latch is a DZ that I mounted 1" off center for better access. The lid is sealed with adhesive window gasket. The box extends about 2" deeper than the frame rails and gives plenty of room for all my stuff.
