Eberspacher D2 diesel heater for sale, as removed from Serenity 4 months with most bits for installation, will need some ducting. I have had this working on the work bench since removal and have renewed the glow plug.
£100
Call Tony on 07733101037 to discuss
Same for me , antifreeze in the heat exchanger , drain fresh water and remove shower head, small electric heater in the cabin over the cold part of the winter. A dehumidifier is useful to catch condensation.