They are not universal, each manufacturer is different. Mine mounts to the bed by way of the receiver of a gooseneck assembly and has well distributed pads that contact the bed of the truck, but aren't actually attached. That is why I can change from fifthwheel to goosenech just by pulling one pin ubder the bed. The receiver assembly is mounted to the frame with bolts through the frame an u-bolts around the frame,IIRC.
