try this one: http://www.amazon.com/gp/product/B000FI6WSG
u can attach the rack anywhere on the seatpost (as long as the trunk bag won't hit ur seat). and it would be best to get one of their many rear bags that is designed for this rack...quick slide in and locked.

btw...what train are u on that u have ur own private compartment with leather seat? amtrak? if so, what route and how much was the fare?