After spending what likely was too much time investigating possible camera bags and how I would use them while travelling eventually decided to order an Ape Case
Cubeze QB35 Flexible Storage Cube that I can use in different day packs, slings or backpacks as the situation dictates.
The greater flexibility and value, the QB35 is $25 with S&H, were strong deciding factors as I wanted to keep using my Eddie Bauer day pack which has proven a reliable travelling companion on lots of trips over a decade.