Yeah under my front bar is really bad with scratches from before I bought it, I think from not taking gutters at the right angle. One of these days I'll sand it back and re paint it or use a trick I've seen some lowered bodykitted cars use. They blend some metal (tin or alloy sheet cut to the right size) to the underside of the front bar and side skirts with fibre-glass. You can't see it because it is underneath but it stops the scratches on the bodykit. Maybe kevlar or something might be just as good as well, I'm still to look into it.
Though I've only sctrached it myself once since I've had the car at a really nasty driveway that I couldn't get any angle on, I don't use that driveway anymore suffice to say.