I would look at getting a Capture Camera Clip System http://peakdesignltd.com/
(also on amazon). It attaches to either your belt or the arm strap of your backpack. It securely holds your camera to your backpack and makes it very easy to retrieve. After a few minutes with it on your belt or backpack strap you won't even notice it. I've used it hiking Yosemite and have had it on all day and it was much more comfortable then a neck strap or having to retrieve my camera from my backpack constantly. The plate that attaches the camera to the clip system is also compatible with the Joby Ballhead X tripod head, a very lightweight yet good quality tripod head that may be a good choice for your trip.
If you do go with this I'd replace your neck straps with hand straps for your camera bodies. I'm sure you'll enjoy the clip system.