A practical question about travel in late 20s/early 30s

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I'm writing a fic (a sequel, actually), in which Bertie and Jeeves travel from Brinkley Court to the South of France. This leads to questions, which I hope someone in this lovely fluffy community can help me out with, even if it's only a guess.

1. How long would it take to travel from A to B in that pre-Channel Tunnel era?

2. Would they mostly travel by train, do you think?

3. If the journey is more than 12 hours, and they left in the afternoon/evening, would they stop overnight somewhere on the way, or would they sleep on the train? Did they run night trains in France, then? Is it likely there'd be a train leaving in the late afternoon for that destination?

4. Was there a train that went straight from Calais or Boulogne in North France all the way to the south?

You get my basic idea, I think. What are your thoughts? Anyone know much about 1920s travel?

Thanks very much for any help you can give.