Earlier in this thread, Mike (pelorus) recommended the Ortlieb Atrack backpack. I was intrigued because it seemed to have everything I was looking for (water proof, good harness, lots of room, simple, flexible). Mike had the 25L model, which I thought might be a bit small. Thanks to his enthusiasm and helpful advice, I decided to try one of these in 35L.
I wanted to update this thread not only to second Mike's enthusiasm for the Ortlieb Atrack, which is really excellent, but also to showcase a solution to my layout problem that may be relevant to other people. In a nutshell, I wanted to be able to carry an assembled Toyo VX23D digital view camera. These cameras are extremely sturdy, but they don't pack easily, and the bellows they use -- while tough and durable -- need to be protected. I didn't want to have to disassemble the Toyo every time I needed to carry it anywhere.
I looked at all kinds of inserts and decided the best way to go was to build my own. The product I used is called "Kaizen Foam". It comes in all kinds of colours (not just the rather unfortunate yellow that I chose). Kaizen Foam is normally used by people who want more organized toolboxes. You draw out the shape of your tool on the foam, cut to the required depth, and peel off as many layers as needed. I used 3 layers of the 57mm thick foam to build a protective enclosure for my Toyo VX23D and Fuji GFX50R. The layers are glued together with 3M 77 spray adhesive. Everything else I need to carry (lenses, bits and pieces) travels in the backpack in its own protective case or pouch.
Here's what it looks like loaded up. There's not a lot of extra room, but I can fit in some clothing, food and water. This is not a setup for overnight hikes.
The main piece of the foam insert holds the Toyo, while a "peninsula" of foam juts out at the top and holds my GFX 50R. The lenses are loaded in the empty space around the 50R. Both the 50R and the VX23D are locked into their compartments because of the snug fit. I can pull them out with one hand, but when they're in their compartments, they're so secure that I can lean the pack forward and they won't fall out; the lenses will of course tumble to the ground because they're loose, so I don't lean it forward open...
The space for the VX23D is fairly complex. I used a stack of three layers of the 57mm foam so that the entire camera would be below the top. One end of the rail plugs into that round hole; the weight of the camera is shared by the rail hole and the tripod clamp, which rests on a layer of foam at the bottom. I left room for my compendium shade at the bottom of the space that holds the VX23D. Currently there's no solid bottom on the foam unit, something I'm going to remedy by gluing a layer of corrugated plastic to give the compendium a bit more protection.
Building this insert took a while, but mostly because I didn't want to have to re-do it so I took my time. Cutting and gluing the foam is extremely easy once you know what you want to do.
From this position, I can lift the VX23D out of the bag one-handed and have it on the tripod ready to shoot once I add a lens and the Fuji GFX 50R.
Big thanks to Mike for his pre-sales advice!