Not to substitute what you are planning, but may be a good addition to proivide more options is to add an inexpensive draw-string foldable backpack (folded) in the car. It gives you (or family memeber) the option of grabbing some stuff from those scattered material to form an addition BOB on the spot, if you need it.

The philosophy of scattered stuff is great and I do that to my office bug-in kit. But you need more options if the stuff is in a car. Say, you drive and reach somewhere , where you have to go in a shelter or hotel, and need to have the bag and stuff with you.