I have the molded mopar flaps as well and they really look great.
As for as drilling is concerned , the rear flaps really dont require the hole to be drilled out because it is between 2 other screws that secure the flap into the wheel well. (I drilled it anyway)
The front flaps really should be drilled and screwed because that hole is located all the way at the top edge of the flap, without this screw the molded plastic can gap away from the fender.
edit: see the PDF installation guide for the front flaps here http://www.mopar-accessories.com/en-...=3163&pc=64701