Don't try to take two cases - your standard soft case should be good enough.

I use a LowePro backpack. The back of the pack (the part that actually touches your back) has to be pretty thickly padded to protect your back from the contents of the pack. The camera itself goes in the middle of the pack so the edges are protected by the stuff placed around it in the pack. The, I fold my darkcloth and place it over the camera to protect it from anything that might strike the front of the pack.

The one area that I was still concerned about was the ground glass - the only thing between it and the outside world was the folded darkcloth and the fairly thin face of the pack. Years ago I you could buy commercial plastic shields that fit over the ground glass panels of field cameras, but I haven't seen one for years - so I cut a piece of plexiglass to fit over the ground glass that attaches to the camera with velcro and that shields the ground glass from outside objects.