Setting the rivets for your D rings shouldn't be too hard in that geometry you are showing...I use a 9 pound hobby anvil...they are pretty cheap. Is your question related to rivets inside the holder pocket (not shown)? I used to fuss with that problem on cell phone cases too...anything with a throat depth of more than a couple of inches is a problem when you are trying to close the bottom...I have a couple of ideas for you (like the radio holder and the theme by the way) but I kind of need to see the exact problem...the rivets you are showing in your photo, in my opinion, are the best application.
I'm watching the work of a few of my online peers and noticing that they are going to great lengths to stitch up straps and casework, but not really lining the leather and not for obvious structural or assembly reasons. I've certainly stitched my share of works but only if I was lining a piece or making a connection and on the rarest of occasions for an aesthetic effect. Does anybody else on these forums do this? Is there some function other than "looks"? Particularly the straps---does stitching prevent stretching and loss of shape over time? Thanks for your thoughts. Mike