For the last 30+ years I have been using the Brady Ariel Trout fishing bags. They are built like nothing else. Water proof insert for carrying live trout home - if I happen to run into one.
They last me from 3-5 years after which the "duck" canvas usually has worn out on the side that hangs against the pants (and also worn out at least 2-3 pairs of jeans!
I don't use inserts - they take up to much room. I keep a "happy" towel (japanse idiom) and use that to pad between camera bodies. It has two front pockets for pipe,tobacco and matches as well as the odds and ends we keep dragging around. Film is in film cans taped bottom to bottom.
The design evidently harks back to the 30's - all good leather straps and brass lugs, wide canvas strap which I modify either with a pad from a Domke or simply stitch in a piece of leather with the rough side down to eliminate slipping off the shoulder. Also can hold a couple of magazines, a thick pocket book etc. It can take 2 M/Bessa/Nikon Rf bodies and an extra lens. One body is usually around my neck anyway.
Rumours have it that Billingham was started by someone who worked for Brady at some time. They have gone a bit upscale now with a choice of colour - but I stick to the canvas colour out of habit.