I just replaced mine and this is the correct answer. It's not difficult, but it isn't as easy as replacing the bottom strip. Here is the new weatherstrip as it came to me:



The first thing I did was roll down the back window. Then, you need to pull out the bottom windowstrip piece, which comes straight up.

The old weatherstrip was held in pretty well. So the easiest way for me to pull it off was to start halfway up one side:



With that loosened, I could slide the bottom up and out:



It was quite dirty underneath, so I cleaned it up using a spray bottle with four parts water to one part Simple Green:



Here's a look at the inside channel on the bottom corner:



As you can see, the window is well out of the way once it's rolled down. On the left side of the area you can see circled is a tab the weatherstrip will need to slide along. Just to be clear, the left side of the photo is the outside of the vehicle.

I did notice what appeared to be some sort of caulk/adhesive inside the channel of the old weatherstrip where it contacts the metal of the door. I don't know if this is a factory thing or an attempt at leak repair in the past:



But I can say my old weatherstrip looked pretty good overall. So if you're having problems with water inside your tailgate, I'd definitely follow the advice of others on the forum and replace the bottom strip only first and see if that fixes the issue.

At this point, it's just a matter of finagling in the new weatherstrip. I started at the bottom corner of one side. There is a piece of the weatherstrip that extends past the window and needs to slide down into door. Squeeze outside and inside edges of the weatherstrip together so you can tuck it into the channel in the door.

Work the weatherstrip in a few inches at a time so the sharp edges of the door don't cut it. Go all the way up the side, get the top corner in, then go about a third of the way across the top. Repeat this process for the other side.

You'll now have a section that droops in the middle that you'll just have to be patient and work with to get squeezed up into the door.

Sorry I don't have pictures of the this part of the process. Though it is a one-man job, I had to use both hands not just to get the new strip in, but to keep it from dropping back out of the channel as I was working with it.

Here's the door with new top and bottom weatherstrips.