They are the best clips available with the little gaskets on them.
Put the clip in the body, slide the peg into them flush.
Put the strip on the lower part of the clip and whack the top of the trim over them with the palm of your hand. They are tight but good. If the panel has any bodyfiller in it then the peg will be very tight to insert. I sometimes run a small screwdriver around in the hole to make sure there isnt any muck in there. Be careful not to take any paint off though.
Cheers and good luck, Andrew