Any hints as to how: a) tell via the amtrak website whether a certain route will more than likely have a sleeper available for an onboard upgrade
b)how and when is the best time to ask the conductor about upgrading to sleeper once I am aboard c)at what rate would the upgrade be?... the lowest fare available on that route for a sleeper OR the same rate as if i would have booked the sleeper the day before my trip?

THANKS!