So, I felt there was enough potential with that paper backed denim to give it another shot. This time I tried to overcome the shortcomings - weak backing material, fraying - by using a sturdier paper, and folding in the edges. 

note the cute crochet lace ribbon. only 50 cents a yard!

It's a lot more solid than the other book, but it's still very rough around the edges.  Basically any spot I didn't fold over has loose threads.

244 pages of blue, linen textured text weight paper btw

I ironed it after pasting to dry it smooth, but then when I applied the liner on the inside it wrinkled again, and this time despite ironing I just couldn't get that wave to go away. You can see a little of that here. It did make it VERY sturdy though. Not as stiff as actual boards, but stiffer than, say, a paperback cover.

Oh, another thing I discovered is that when you fold the cover to make the spine, the liner will separate away from fabric and wrinkle and it was just a real pain in the back. I'm not sure what can be done about that.

not sure how exactly this happened

Another unexpected difficulty came in the sewing. Normally when I sew I can find my punched holes pretty easily, but when you pierce fabric this thick apparently the threads come right back together. It made it VERY difficult to get the needle back in from the outside. It ended up.. a lot more uneven than I like. Oh well!

It was a good learning experience. I have a lot more ideas to try re denim and books, but I'm pretty sure now that the heavyweight denim I used here just isn't gonna work out with paper backing. We'll see how the next thing turns out!