An assembly and process for forming a two stage extrusion of an elongated marine dock from a plasticized material, such as including but act limited to extruding a first generally “L” shaped bracket from a first more rigid thermoplastic, following which a cross head die arrangement is utilized in order to extrude a secondary arcuate and flexible material in extending fashion from a lower side of the “L” bracket. The secondary/flexible elastomer is extracted in an open flexed position relative to the first extruded bracket, and further such that, following completion, can be flexed into a closed engagement with an upper perpendicularly extending side of the bracket.