Load support structures for mounting a load atop a raised rib metal panel roof make use of relatively small, inexpensive, and easy-to-make adapter plugs as interfaces between the raised ribs and one or more component pieces or members of the load support structure, such as an upper diverter or a lower closure member. The adapter plug has an inner surface and an outer surface, the inner surface having an inner profile substantially matching or conforming to some or all of the profile of a particular style of rib profile. The outer surface of the adapter plug has a standardized shape, some or all of which is made to conform to an upper diverter, lower closure, and/or other component member of the load support structure.