Hmm, I'm not sure that I would trust my car for that trip either, not without an AA membership anyway.
Is this another Citroen gathering I haven't heard about ?
I really must try and get to one that's within drivable distance one day, this one is bad timing falling as it does in the middle of moving house, plus I would want to get a few more things done (including engine/gearbox oil changes, and AA membership!) before considering a trip of that length.
My previous Xantia was reliable to a T, and I wouldn't have even hesitated to drive a 400 mile round trip to far away places in it, but not this one! At least not with a dodgy gearbox.