Ive had the chance this past summer to field test over a dozen hiking backpacks for photography outings and 6 of the best photography backpacks for something I am putting together and it really confirmed what I had thought in the past... that none of the photography backpacks made really stand up to hiking backpacks for all day comfort, carrying the extra non-photography items needed on long outings, weather sealing and ruggedness.
Please keep in mind I am a wildlife photographer who spends days hiking and in the field so this may not be the best setup for urban street photographers.
That being said none of the hiking backpacks had what I thought was a secure enough compartment for my camera gear so I did as u did and looked for something to put the cameras in.
A freind of mine who owns an ecotour company which specialises in guilded zodiac tours on the ocean and who is also an avid photographer has used dry bags forever to hold his cameras and camera gear.
The pack I have now has a side access lower compartment and what I have done is bought 2 dry bags, lined them with a sheet of foam padding 1/2 inch thick and I keep my cameras in there. On nice days with no threat of rain I just leave the drybags open in the backpack so its fast access by just opening the zippered backpack compartment and pulling out the camera as quickly as any photography based backpack. When on the water or on rainy days I close the dry bags and even if I fall in the water or get caught in a down pour I know my gear is completely safe and will stay dry no matter what.
I've also adapted 2 black rapid camera straps and attached one to each of the backpack shoulder straps so when hiking on nice days 1 or both of my cameras are at the ready at my hips for instant shooting. I am really surprised none of the big photography backpack companies have included this idea on their packs as it completely changes your photography outing and how fast you take your pictures. No more diving into bags to get your camera for a fast shot... the camera is always at the ready.
Here is a link to one type of dry bag/dry sack but there are many varieties out there.
Just some ideas to consider but they are not for everyone.