The absolute hands down best bag for the Saab is the Pelican 1510 (even better with the optional Pelican 1519 lid organizer). It is indestructible even when dropped from chest level out of the back onto the ramp. 100% waterproof for when they leave it out in the pouring rain or spray deicing fluid on it, or the fish crate breaks open and soaks everything in the cargo hold.
Just get a J-hook and screw it to the bag, epoxy over the screw and you have the best of the best for the Saab!
http://pelican.com/cases_detail.php?Case=1510
It does fit in the bins of all the NWA mainline aircraft for commuting or deadheading purposes.
http://pelican.com/airline_allowance_medium.php