So I started stripping paint from the driver's rocker panel and came across some corrosion. Since I'm new to the body and fender world, I'm not sure how to handle it. Do I replace it or can stop it with some type of chemical? Need help.
This is what I would do before using any chemical treatment.
What would concern me is what's on the OTHER side of the metal he can't see. Rust is some evil stuff and will eventually come back to haunt you if you don't knock it out. If there aren't any holes through the metal after doing some spot media blasting, then he should be fine with just media blasting and then epoxy primer. But I would cut out and replace any areas that have visible rust holes with new metal. Hopefully it won't come to that, but a few small matches are easy to tackle.
Now that the cat is out of the bag you have too many pits there for moisture to sit. You can treat it with chemicals, rust stop, vinegar or whatever but it WILL come back. Rocker panels are subject to any and all types of conditions, like weather, flying bits, moisture etc etc.
I would only consider new steel if you don't have a professional paintbooth available where it can sit hot and dry for a week before you reseal it.
After what I have seen other members do, replacing a rocker panel is not an impossible job. Some guys have replaced entire frame rails, entire roof panels, etc. So I wouldn't be afraid to tackle a rocker panel.
I am sure there is a write up in this forum about how to do it right. Ultimately you are going to MEASURE, MEASURE, MEASURE and then brace that area (front-to-back and side-to-side) since rocker panels are structural. Then it's a matter of cutting all the spot welds. I am greatly simplifying this process, but it can be done with proper planning and patience.
I would also look into replacing the rotted section with a piece from a donor car. Do you have pics of the rotted area?