For front flaps I originally had some OEM copies. But they would occasionally catch on even low kerbs, and the near side one eventually broke so I replaced them with genuine OEM ones. The rubber was noticeably more flexible so hopefully they have more give in them and will not fail. If I remember correctly, they use existing holes, but I did use a riv-nut in the underneath hole instead of the rubber grommet that came with them.
For the rear, I have fitted moulded ones, but I can’t remember whether I had to drill a hole in the wheel arch liner for them.