I use these boxes:
Serious anglers now have serious storage. This high capacity box will easily hold your largest streamers and bass bugs down to any standard dries & nymphs
www.umpqua.com
i agree, there is not a perfect box out there for what you describe, but these are dang close. They aren't cheap, but they are durable, both inside (the foam), and out (the plastic). I don't get much mashed hackle on my smaller dries, which I put on the side with the blank area in between the foam pieces. And then on my chubby style flies (mostly sans hackle) I put them on the full foam side. The foam is deep enough, and the lid is high enough that if you think you are going to mash hackle, you can angle your flies up a bit. They are kind of bulky, but woukd hold enough flies for a multi day backpacking trip. They are probably 2.5" deep (1.25" on each side), and then 12" x 7" (just a guesstimation). In my day trip backpack I carry 2 of these, along with 3 of the smaller versions of these, and a little one sided streamer box. This leaves room for 4 beers, some snacks, a water bottle, and then all the floatant and tools and stuff. I likely carry more than the average fisherman, or the many minimalists that seem to be on this thread, but I don't like to take shortcuts, and I like a wide variety of flies. I think you would be pretty happy with 1 of these. I've been using the two of them for the past 5 seasons and, while scratched up a bit on the outside from rubbing against each other, the foam is still super tight.
Here are a few pic's of me wearing my pack with the 6 fly boxes, x amount of beers, a water bottle, and some other stuff inside the smaller pockets and hanging off the pack.
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This was in October, and i was even able to jam a jacket from the morning in there. Didn't quite fully zip, but that is what the blue thing emerging from the top is.
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