This tutorial comes by way of Jeff’s facebook group “Traditional American Craftsmen”

There were a couple of questions regarding strap and flap attachment on the bag I'm working on currently. Here's what that looks like before sewing. The strap ends are actually sandwiched between the back panel and flap, creating three layers of hide across the top edge. You can see that I've also added a 1/2" wide strip of the same 3oz veg tan between the straps to give the bag some extra rigidity, avoiding that sag you see in a lot of old bags. I've also punched a hole in the outer corners of each strap, providing a handy tie off point for a vent pick, powder measure, etc. (another tip I learned from Vincent Louis Alessi) I'm not sure if there is documentation of this on originals, but in my experience, it is a useful detail to incorporate when constructing bags in this way.

Something else to note perhaps, I use less stitches per inch, normally around 5, when sewing this top seam, as more tightly spaced stitching would be more prone to strap failure, as stitch holes are in essence a perforation of the strap...