Originally Posted by
DanK
That's my drill as well, except that I only use the Cotton Carrier when I expect to need the camera frequently while hiking. As much of my hiking is in a forest preserve, I don't often need it. I just leave everything in the backpack until I come to a viewpoint, by which time I am usually so tired that I welcome the rest time added by taking off and unpacking the pack.
However, I don't do birding. My heaviest hiking load would typically be a 5DIII, a 25-104 L, a 70-200 f/4 IS L, and a 100mm macro, plus tripod. That is a fairly substantial load, but not anything remotely close to 20 kg.
My biggest problem with this strategy is that I want a separate compartment in the pack for food, etc. I don't want peanut butter or a squashed plum to get into my camera gear. Very few good bags have this, at least if you add in the other things I want, including a good tripod mount, high-quality shoulder and hip straps, a waterproof cover, and a place for a water bottle. I use an old model of LowePro that does have all of this, as well as a very clever system for holding things like windbreakers outside the bag, but its too small--worked pretty well before I went FF--and they don't make anything quite like it now.