I have never seen an additional fender flare for a cladded AV. Then correct way to do a repair of that type is to remove the cladding and patch or replace the rusted metal section then reinstall the plastic cladding. That of course can get expensive depending on how much rust you find. Just covering up with paint/plastic/bedliner etc. is like putting a Band-Aid on cancer besides if you do it right now it may only need a small area patched but let it go or just doing a cover-up could lead to a big expense and problems later.