Jeff, thanks for the feedback. Agree with you on the rivet use for the side loops. I stitch my shell box holders by hand because of the small length of the stitch runs and seems easier than bending the box over on my machine to sew it! I made one of these for myself about 6 years ago and use it 1-2 times a week and other than looking a little beat up, it is holding up great, so I don’t think you would need rivets at the top edges. (I don’t glue the sides before stitching - just prepunch the holes and stitch them up.)
Gary