The reinforcement plates

You should now have the trim panel resting with the insulation facing you.  The next step is to remove the fasteners.  Remove them carefully, as you may need to re-use them.

Here is the fastener as installed:

Rotate it 45 degrees.

You can now remove the fastener.  Now that you can see underneath the fastener, aren't you glad you supported the weight of the panel?

The repair kit consists of: four metal plates, four new black plastic mounting tabs, and some screws.  The metal plates reinforce the plastic of the trim panel where the plastic mounting tabs insert.  These are bent around the mounting points on the trim panel.  The plate on the left is as it arrived, the one on the right is after I bent it to fit the mounting point.

The flat reinforcement plate will only fit one way on the mounting point.

Bend the tabs around the mounting point

Make your life easier by drilling pilot holes,

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before installing the screws.  Don't drill all the pilot holes at once.  Drill a pilot and then set the screw before drilling the next pilot hole.  The hole on the metal plate will shift as you tighten the screw.  The vendor thoughtfully provides a few extra screws, just in case.

There was a recommendation on Brickboard to put some silicone goop on the tabs that insert into the mounting point.  Sage advice, as the source of the rattle may indeed be the tab bouncing about in the mounting point.   Can't hurt.

The mounting tab as installed in the trim panel, along with the reinforcement plate.

But first do the 'might-as-wells'.  Then take a break and have a cuppa.    It's a little frustrating getting all four black tabs lined up with the slots.  You'll want to tackle this part with a clear head.    Try first by sitting inside the cargo area & fitting the panel with the door closed.   If you look at the glass, you can see reflection of the black tabs.  The reflection will help you to align the tab with its slot.  It's going to take several tries.  Be patient.   If this proves frustrating, try with the tailgate open.

If you are working with the door closed, re-set the long black screws at the latch lever. 

If you are working with the door open, have the interior-coloured fittings for the lower part of the trim in your pocket.  Once you have the upper tabs set, take a fitting from your pocket and use it to anchor the lower part of the panel.   Keep supporting the panel with your hand until you have at least two fittings in place.  Then you can re-set the long black screws at the latch lever.

The lower part of the panel was a bit loose.  I sliced up some grommets and placed them as shims between the trim panel and the steel of  the tailgate. 

Also one of these beige fasteners was missing.  Remember the broken fastener from the top? 

Perfect fit to replace the missing fastener.