if the rockers are bad/getting/bad you might want to check the floors also.
4 doors are a little more difficult to replace the rockers on, if you do the original sheetmetal replacement. basicly more spot welds to cut and weld back up. Any sheetmetal work on Cherokees can be a pain because of the spot welds and bracing to make sure that the unibody doesn’t move.
The Box steel rocker replacement has been done and looks pretty good, the basic concept is to leave the very top of the rocker/door jam and weld in the box steel. For this to be useful you also have to brace the box steel to the inner “frame Rail”
your best bet is to search on Naxja or jeepforum for more information and pictures
the floors are notorious for being junk under the carpet.
i bought a jeep with half decent rockers only a few holes, pulled the carpet out and it was piled loose rust, by the time i banged it all out, there wasnt much of a floor left.
Google Rock Sliders for jeeps and there are several pictures out there. Some of the pre-made ones are for below the rocker panel, but there are some decent DIY ones.