I had put a Dowco Overnight bag on my Savage.
It is much lighter than a plastic trunk and does not cause the luggage rack to flex when going over rough pavement.
I fastened it to the luggage rack by placing a sheet of aluminum in the bottom, drilling through the bottom and placing a carriage bolt and fender washers through the slots in the luggage rack. It worked well. It's big enough to carry a laptop and some other small items.