Originally Posted by Dunbar

The Eagle Creek Adventure Weekender is the same dimensions as the Sky Train. That's another option for a less expensive alternative to the Tom Bihn / Red Oxx luggage.

If you go the eBags route I'd highly recommend the TLS Motherlode Junior. I have the full sized Motherlode and it's too heavy to comfortably carry on your back when it's packed.

BTW, the Tri-Star is quite a bit smaller than the Aeronaut and Sky Train. I have an REI Overnighter that is roughly the same volume as the Tri-Star and it will not carry as much a bag with 10-30% more volume.