A couple of years back I had stumbled across a light recipe for making a 3D book from a book cover design in GIMP. I did this for the Drift cover. It was a struggle, as I remember. I thought the results worth it, to make a marketing statement.
When it came time to make the covers for the other titles, I tried to replay the technique from memory. That was a struggle. I kept notes this time, refining the process, keeping the layout numbers organized- revision after revision until I finally got it. I did the other titles and redid Drift as well. All were left with the layers un-collapsed, the 2D and 3D in the same *.xcf . Guides are wonderful. Don’t overlook using them.
Here’s the notes and some *.png referenced, if you want to play. Just supply your own base picture.