The bottom of the box. Here you can see the seams. It took me two pieces to go all the way around. Try to make your seam or seams on the straightest part of your box, and overlap the side pieces when you tape them together.
I fringe the tape along the edge of the new side strip leaving about 2 inches without tape to tuck inside. Then I tuck it in and tape the side pieces together, making sure to lap the tape over the top and bottom edges, and then continue pushing down the fringe around the rest of the bottom. When I get to the end, I tuck that end inside, too and tape the seam.