This tutorial is meant to pair with the BONUS LAYOUT for the Road Trip Quilt Pattern (as shown in tutorial). You can however use any quilt top front that measures to 24ish". Additionally, you can use the techniques here and adjust the sizes as needed. 
Materials Needed
(1) 25" piece of backing fabric- for back of pillow (24.5" if not planning to quilt it)
(2) 26" pieces of batting (only 1 if you don't plan to quilt the back, I do highly recommend quilting it however)
(2) 26" pieces of muslin for the quilt sandwiches (only 1 if you don't plan to quilt the back)
(1) 22" zipper (I use cotton with metal zipper). If you use nylon then at least 24", but longer will work since you can cut it to size.
(1) 5" x 5" coordinating piece of fabric- for zipper tabs
A piece of fusible hem tape about 8 to 10" long
Let's Get Started
Prepare the zipper (if using a nylon zipper, trim it to 24" and skip the fabric tab steps).
Sew Zipper in Place
Unzip zipper about halfway and lay, face-down, right sides together, along one long side of the 9” (smaller piece) wide pillow back panel, being sure to center it on the panel, leaving roughly 1/2" on either side of zipper. Pin or clip in place.
Using your zipper foot, sew zipper in place (backstitch at the beginning), removing clips as you go and stopping an inch or so from where zipper is closed. With the needle down, lift presser foot and close the zipper.
Finish sewing zipper to the panel. Backstitch at the end.
Finish the raw edge by zigzag stitching the entire length of zipper through all layers.
Press quilted panel down, away from zipper (I forgot to get a photo of this step) and topstitch along the edge of the panel right next to the zipper.
Next, place the zipper piece right side down on the top of the other half of the back piece.
Pin in place.
Repeat the process you used for the first side of the zipper, in order to attach the zipper to the other side of your pillow back.
Once both sides have been topstitched (as shown above, but hard to see),
lay the front piece on top of the back as a guide to trim away any excess batting or fabric from the back piece top and bottom. If the sides need a little trimming too, now is the time. They should be the same size and match on all four sides.
Unzip the zipper about 2/3 of the way and place right sides together (this step is critical- I promise). Pin or clip all layers together. Stitch around all sides, using 1/2" seam allowance and backstitching at each corner.
Instead of pivoting at each corner, sew each side from edge to edge. Trim about 1/8" away from the point where the side seams meet.
Optional step: Sew a zig zag stitch all the way around the perimeter of the pillow. I often forget this step but it's a good one.
You have finished your pillow! Yay! Now you get to turn it right side out, push out those corners and stuff that fluffy, oversized insert in there.
Nice job! Give yourself a pat on the back!!