I know from experience that the backpack isn't a friendly place for less-durable materials.
This is why I store models in boxes with jigs as needed to hold everything in place. For small models, these boxes can be very small, especially if the tail surfaces and landing gear are removable.
A side benefit of storing planes in boxes is that hangar rash is minimized.
Space is another factor. When you have as many planes as my wife and I have (we've stabilized around 100 airframes, and are looking to sell off a few), space becomes a major issue. Most of our planes stay in a small room, with some boxes containing 10-15 small models.