I didn't find markings on mine but they fit best with the flat part at front, tucked under the seal. Grey 1/2" 3M attachment tape would be my first choice. I used black because thats what was on the shelf. After getting a good stick to the rail, peel back the ends of the tape liner a little and leave the ends hanging out where you can grab them. Position the rail and lightly stick the ends then pull out the tape liner once you're happy with the fit and press it all down hard. Next few times the car is warm on top, maybe mash them down again and wiggle to test for looseness as a re-check.
