Closing in the sides of the Coroplast tailbox
Now we close in the sides. By now you should be pretty good at poking holes in Coroplast, zipping up zip ties, and making cuts in Coroplast. You’ll use all these skills for the sides, so be thankful for the practice. Also, you get to hide all the mistakes you’ve made up to now.
Cut two pieces of Coroplast 17" x 26" with the flutes or grain running parallel to the long side. Also cut two pieces of PVC pipe about 9" long.
If you haven't already, cut the bottom pieces along the curve you marked off in Step #1. Using zip ties, attach the PVC pipes to the sides of piece #1, about 2" from the rear edge. These will brace the rear edge, so they should end up sandwiched between the inner and outer surfaces.
Line up the outer panel so that its lower edge protrudes about 1/2" below the bottom (horizontal) piece. Starting from the front, stitch the outer panel to the bottom panel, wrapping the zip under the bottom edge of the outer panel, like this: . Once the zip ties are pulled tight, the outer panel will curl under the bottom panel, forming a continuous seam.
Where the outer panel meets the front panel (piece #2), connect the pieces with zip ties forming "Tee" joints: . Also do this where the outer panel meets the lid.
Stitch the outer panel to the inner panel where they meet at the rear, using zip ties looped behind the PVC pipe you attached above. The joint should look like this from the rear: . Pull everything tight and trim off all of the excess zip ties. Repeat for the other side. Trim off the portions of the outer panels that stick out in front of the seat.
Cut a piece of Coroplast 6" x 12" with the flutes running parallel to the short edge. Crease this 3" from each short side and stitch it in place at the rear to fill in the gap between the two outer panels. This is where the latch mounts. This is also a good place to mount an LED blinker or reflector.
Cut a pair of slots in this piece and another slot in the rear flap of the lid. Thread the toe strap or straps through the rear piece and out through the flap. This makes a secure, low-cost latch for the lid.
The patterns (click to enlarge):
The nearly finished product. This is with the bottom and rear edge tied in place, but before the front portion of the side panels are cut away. The front edges of this panel will end up about 1” behind the seat frame.