Abstract: An assembly for the production of covers, or toppers, for the truck beds of various sizes and makes of pick-up trucks comprising a preformed shell which serves as a base or body portion for the finished cover, and a support member for the preformed shell which provides means for trimming the shell to a predetermined length and enables the shell to be maintained in a fixed position during fabrication of the completed cover. The preformed shell has an initial length greater than that of the finished cover, and, together with the support member, provides a simple, effective and efficient means for making covers for at least eleven different models and makes of pick-up trucks.