You can see how the zippers lay much flatter in the purple/blue one. I laid the vinyl on top of the zipper instead of right sides together. I wasn't a huge fan of this because you have to be careful that the vinyl is close to the teeth but not so close that it prevents you from using the zipper. Important- the edges of your vinyl need to be VERY straight! I'm usually a bit willy-nilly when I cut my vinyl but this time I wanted it to be as perfect as possible. I cut a large square of vinyl and laid it on my gridding. Using masking tape, I delineated the 4" and 8.5" marks for as many pieces as would fit (you need 3 total). I used a pen to make an arrow to indicate which edge of the masking tape I should cut from. It wasn't perfect-perfect, mainly because some of the vinyl was bent from being folded, but it worked out pretty well!
Another option would be right sides together for every piece, then top stitch the bottom edge of zipper to lay flat. And then to attach to the fabric top stitch the top edge.
I didn't like how long and how thin the straps were on the orange one, or where they were located. It didn't make sense to me. So I made them thicker (1.5" wide, then folded). I ended up sewing it to the middle (measure!) of the back piece. So, if I had planned to do this from the beginning I would have just made one long piece. I also decided to do this after I had put everything together, so I carefully hand sewed the straps on.
If you want to do straps like the blue one, cut a piece of fabric 1.5-2" wide by 30" long (you avoid having to join two pieces like mine). Then stitch to the center of the piece before you bias sew the edges down.
Do you find yourself measuring twice-cutting once and sewing extra carefully when you're sewing a gift for someone versus sewing for yourself?