take it to a reputable body shop and be ready to pay good money for a quality repair. what hj posted isnt a replacement rocker panel, it is a stainless steel accent plate to stick onto the vehicle. proper rust repair is very time consuming and expensive and there are 2 ways to go about it. one would be to replace the rusted panels with entirely new ones if possible, (this is the best way). the other would be to cut out all of the rusted metal and patch in new material, (this can be equally effective but will take a lot more time and skill. in either case the repair has to be painted and blended with the rest of the paint on the vehicle. most people do not have the proper skills, knowledge, or equipment to handle something like this at home. so as i said before, find a reputable shop that does good quality rust repair and pay to have it done right. to prevent rust in the future i would recommend using a cavity wax or fluid film on the inside of the rockers and keep up with routine cleaning (especially areas where dirt collects).