Note, the splash apron rubber pieces were originally stapled to the inner fender wells. As JohnZ pointed out, be sure to purchase a copy of the assembly manual as it will show you exactly where and about how many staples to use. Itís not easy to hold the two pieces together and drill thru them to install the staples, and to fold the staples back to as they were done originally with the specialized staplers used at the factory, but take your time and your can get nice looking results. If you are restoring your original inner fender wells, then you will have the staple holes in place to use as a guide.
Good luck with your project!