Sealing them would make them worse. Trapping water and dirt is exactly what makes them rot. The gladding trapping the water and dirt make them rust out like a pickup with fender flares. Best thing to do is tat kind like the cladding off and put something like por15 or rust protection on even if its the black sealant kind like a bedliner. Then put the rocker cladding back on. Of course the metal would have to be solid 1st not just covering up the rust.