Probably the best solution for this is to try some higher quality folders. They will be much more convenient for weekend getaways.

I've known people with S&S couplers, and they do work well. However, they aren't quick to put together or take apart; you typically have to remove the cranks, derailleurs, front brakes, fork, both tires, cables (although they make separable cables, so this isn't as bad as it sounds), etc. It takes around an hour, although you would likely get faster if you did it every week. And it's the kind of thing you would want to do in the hotel room, not at the train station. The usual use scenario seems to be someone who wants to be able to take a *particular* bike with them while traveling.

What are the rules for taking bike on trains; how small do they have to be? Also, I haven't been to France for 10 years, but I thought you could take full sized bikes on a lot of trains?