Looking at this project and the following pictures reminded me of a camera bag solution I put together last summer. For years I had been trying out many different kinds of camera bags to carry my DSLR with one zoom lens and the few supporting accessories like extra batteries, filters, cleaning fluid and cloth, remote control, etc, but nothing ever worked very well. Bags that hung off the shoulder straps of my backpack were ungainly when I wanted to remove the pack and some of my packs, like my Mariposa, just didn't have the strength of provisions in the straps to accommodate a camera bag very well. I also tried various waist packs, but they always got in the way of my legs when climbing and the waist belt always dug into my back under my backpack hip belt. Also, most of the camera bags were not waterproof and I always thought having to carry an extra waterproof cover for a bag that already had its own material seemed like redundant weight. So therefore my Ortlieb bags seemed logical, except that the roll-down opening get quite cumbersome when trying to access my camera quickly for a fleeting shot.
Then, just by accident, I came across the Mountain Equipment Postman Mini Bag, a very lightweight, lightly insulated, completely waterproof small shoulder bag:
The bag itself as is wasn't very good for unencumbered walking with a camera, but it did come with a whole array of snaps and buckles and hooks and straps that were meant to allow you to attach the bag to your backpack shoulder straps. The bag has four plastic D-rings originally designed for use as the shoulder strap attachment and waist strap attachment, sort of like the 4 D-Rings on the Lowe Pro AW Nova bags. I tried them, but nothing worked.
Then I hit upon a very simple solution: get two lightweight, 3/4 inch wide nylon camera bag straps with two plastic hooks each (I used the shoulder straps from my waterproof Ortlieb camera bags), attach the hooks in a cross fashion to the 4 D-Rings on the bag, and slip into the two straps as you would a camera harness, so that it makes an "X" at your back. Voila! A very simple, very lightweight, and very stable carrying system. I can climb the steepest hills without worry about my camera bag swinging forward, it carries a little above my navel so that it's not too high on the chest or too low over the crotch (you can adjust this), and best of all it carries independently from my backpack, so I can always have my camera with me and the camera doesn't swing down and hit rocks and such when taking off my backpack. I did get an extra foam insert to protect the camera, so that brought the weight up a little. The entire bag with foam insert and two nylon straps, weighs 365 g.
Here are some photos: