Yes, absolutely correct for Northern Climes. If boat is in Croatia then I'm not sure how much frost there is down at Sea Level so freezing water may not be a problem.
Think I'd empty the water tanks anyway to prevent nasties breeding.
Freezing is not a problem here. Sea temperature in winter is not below 8 deg C.
If I leave full Diesel tank I shall not have water condensation in it but I shall have old diesel for next season!?