A simple, two piece slide-on electrical device cover assembly can be adapted for either horizontal or vertical mounting on the same base. Removable rail members that are coupled to the cover through thinned or partially broken or grooved sections enable the rail members to be snapped off under reasonable force. A manufacturer can package and ship a product in a generic configuration and allow an installer to select whether a horizontal or vertical configuration is desired, and quickly adapt and assembly the product for either configuration.