The only problem my 04 C5 had during the winter months was an annoying trim rattle from the ashtray plastic on cold mornings, which soon went. Thats it, nothing else! It just performed as normal, thats what i like to see
Its MOT was also due around Christmas time but it didn't require anything.
I did service it around the same time though, but that was easily bearable. I dont mind being out in the winter weather doing car jobs. Im happier when i dont have to though
Christmas of 2009 me and my dad spent a lot of the holiday outside putting the engine back into the traction and building it all back up. It was freezing, snow on the ground etc. The garage gave some shelter from the cold, it was still below freezing! Was very good though, very worthwhile!
Sounds like your Mégane is a real summer lover!