If you have one, drain the washing machine by removing the cover for the filter. Again if you have one, drain the fresh water filter at the sink - I don't mean the one at the pump - but a secondary filter such as a Seagull that is used to take out any nasties from the drinking water. There will only be a thin layer of water between the housing and the element and being placed high in the boat these are vulnerable to the cold.
I do empty the calorifier using an electric pump and a hose out of the port hole but I fitted a drain cock for the purpose when I replaced the calorifier. Given the level of insulation on the tank I do wonder if it is worthwhile.