Overnight Trains: Can I upgrade once onboard?

Question

OK, my boyfriend and I wanted to try Rick's method of purchasing a couchette instead of a double sleeper on an overnight train to save cash. However, if for some reason we don't, uh, mesh with the people sharing our couchette, can we upgrade to a sleeper enroute, if there is one available? Will the upgrade price enroute be so exorbitant that you would recommend just biting the bullet and buying a double sleeper to begin with?

Or, scenario 2:what if we try to just wing it and sleep in an empty compartment? Do we have to buy our sleeper reservation beforehand, or can we just take a chance and if we have no luck, buy it on board?

Answer 1

Yes unless your in the west then no.

no unless your in the east then yes.

no in the south and no in the north.

yes but only on tuesdays, and every other friday

Where are you talking about?