A bracket kit which enables a user to add upright side boards to a trailer which includes a flat bottom with a metal frame extending upward from the sides of the trailer. The bracket kit includes four brackets which are quickly and easily connected to the trailer frame and which include vertical channels into which uprights sideboards are inserted. The upright boards are held in place by the brackets and enable the trailer to contain and haul loose particulate matter such as mulch, sand, gravel or the like.