The never ending quest for the perfect bag. Well, it does ofcourse not exist. We need different bags for the amount of gear we need, how we travel and if we are hiking long distances or not.
I have been struggling with needing a carry-on size for air travel and at destination having an ergonmic, comfortable backpack for 6 hour walks. On top I wanted a dustproof bag in the often very dry mountains in southern Spain.
I am sharing this idea, because I have not seen anybody else doing this.
I use the frame only of an expedition backpack intended for a heavy load. Sturdy and comfortable, not comparable to standard photobackpack. Then I strap on a suitable size Pelicase depending on mission. This one is small enough to have as a carry-on, unstrap it and check-in the frame or put it in my suitcase with my clothes.
If you do not need to fly, and also need more stuff, then you can turn the case 90 degrees and strap on two of them. You can see there's lots of space left both on top and at the bottom. Or, you strap on a soft bag with picnic and other must-haves....
Very modular for size, excellent to carry with expedition grade frame and water/dust/chock proof at the same time.
Works splendid for me.