Good question. I've made one, working on another right now.
Here is my process so far
1. I got a good scan of the blank canadian cardback from raptor
• cleaned it up in photoshop to fix where the card bubble used to be
2. Redraw all of the logos, text, etc in Adobe Illustrator
3. Place cardback character image
4. Print
• each side on premium photopaper for weight
• spray mount together
5. Cut out the cardback
If wanting to do 25th chromed cardback, well that is a different story.
I do graphic design at work, so this is probably overkill
for bubbles, I cheat and make mine openable using storage cases like these