Can I use this case to store hardware and small fasteners without them shifting around inside?

The case itself is a solid shell with no interior dividers—you'll want to add your own organizers, baggies, or foam inserts to keep fasteners sorted and stable during transport.

Will this case fit in a car door panel or under a seat for mobile storage?

At 9.5" x 7.5", it's designed for compact storage. Test-fit it in your specific vehicle to confirm clearance under seats or in door cavities before committing it as a permanent mobile kit.

Does this case have a latch or locking mechanism to keep the lid closed while driving?

Locking mechanism details aren't specified—check your case when it arrives and secure it with straps or velcro if transport vibration is a concern.