I purchased my 97 with sheet metal screws attaching the interior trim to the metal. I have not yet opened it up to see if the kit was also installed or not. I do see that at one time, presumably before the screws, duct tape was used to secure the interior piece. There is a clunck every once in a while from somewhere in the back (might be the tailgate or might not), but no constant rattle.

Here is what I did. I used the kit but the tailgate went loose again after a while. I was tired of fixing a poor design.

I went and caulked the bottom panel to the window with a clear silicon caulk. Now there is no vibation and the whole thing is very strong. At first look, you cannot tell that there is caulk there. If later on I need to access behind the panel, I will just have to cut the caulk with a sharp blade.