The rocker pannel is a welded on and seam sealed part of the main body. You could cut the whole thing off, but it would be more wise to use a composite hammer and a punch to figure out the extent of damage and fix what needs fixed. If However the whole rocker turns out to be rotten you may need to get one from the salvage yard and patch a whole one in. An easier method if you have a video bore scope tool would be to send the probe in and see what it looks like throughout the inside. Either way, if it's one or 2 spots I'd patch pannel it...use ospho on any lite rusting and inside, then rinse and dry and then spray some fluid film inside after your repair. Make sure to ospho your patch panel as well as properly paint afterwards.