maybe you can find some useful tips for sewing on vinyl in these videos:
https://www.youtube.com/watch?v=KY7KuG80u9M
and here:
https://www.youtube.com/watch?v=DzpatS-KeP0
I'm doing one right now for a much younger granddaughter that has a double vinyl side with glitter sandwiched in between, and one that looks like a snow globe on one side.
similar to this:
https://www.youtube.com/watch?v=WPX9hl3hiq8
and this pouch has a boxed bottom:
https://www.youtube.com/watch?v=YD4nIq6Fg8U