slip on rockers

Time for my yearly rocker panel patch job on the 96 XJ and I've decided to look into the slip on rocker panels I've been told about. What I'm wondering is if there are actual rocker panels specifically manufactured to be slipped over existing rocker panels, or do people just get another rocker panel and put it over the old one and call it a 'slip on.'

​If there are specific slip ons I'd appreciate a link as the ones I've found so far seem to be just regular rocker panels.