I been working on a system to carry my dSLR while backpacking. My goals were to 1) keep the weight of the setup down, 2) keep it accessible, 3) provide protection from bumps and rain, and 4) be comfortable. After my last trip to RMNP I'm happy to report I'm very satisfied with the system I used (this has been work in progress for quite a while). I found it met the above goals perfectly.
Here's what it looks like:
List of that pictured above:
Lens: 17-40 L f/4
Extra CF card
Think Tank Digital Holster, size 20 with shoulder strap removed and replaced with 2.5 mm nylon cord, which is threaded through the back side of the holster.
Perfection loops are tied at each end of the cord, and an adjustment loop has been installed (using a Klemheist knot ).
A Black Diamond Carabiner is attached to the Klemheist on one end and the perfection loop on the other end. These clips are attached to the D rings on the backpacks shoulder straps.
During rain the camera and its components are stored in a waterproof dry bag and the holster is covered with the provided rain cover. Photos of these can been seen HERE.
The weight of the holster, rain cover, and cord is 14.3 ounces. The weight of the everything mentioned above is 4.5 pounds.
The setup in action: