Are the rocker panels typically listed on ebay designed to completely replace the originals or go over them?

I thought I saw the answer to this on this forum but cannot find it.

Someone posted a link one to use goodle to search a site, but I cant find that either.

Sorry for the redundant questions.

 

The ones I am familiar with are made by Classic2Current fabrication over in Detroit. You'll find them on Amazon, ebay or factory direct. They make "rust repair" rockers that are made to fit over the factory parts. Cut/grind the rusty sections out first.
There are other suppliers like Sherman, etc, but I've never used their stuff thus can't comment.