I used Herculiner on both sides of my new inner fenders and it worked great. They've been on the rig for two years and don't show any signs of stone chips or anything, no rust at all. They've been put through hell too... getting pounded with rocks, mud, ice, road salt, pretty much anything my TSL's can get ahold of. There's actually dents where the tires launched rocks into the fenders but didn't chip the liner at all. I would have used it under the body too but I figured it would be a pain to try and get at everything under there with a roller, so that got sprayed with regular rubber undercoating.