You'll be fine to leave it connected during the Winter.
However, if it makes you happier, you could just top up the battery charge weekly if leaving the battery connected to the car. Alternatively, take the battery off the car and bring it indoors, the battery would only then need charging monthly, but make sure the room is well ventilated.
I've chosen the third option for two cars currently sorn'ed, and it only takes a few hours to top them up using my smart charger, which has a max. output of 3.8A (your CTEK is 5A).
HTH