My van is long wheelbase, I have a 38 litre CAK tank fitted in front of the spare wheel. I have an Eberspacher 5 Kw hydronic water heater which is plumbed into the engine cooling system and there is a 2Kw matrix blower unit under the passenger seat for hot air heating inside the van, there is a 10 litre calorifier mounted underneath the van to supply hot water to the sink tap and a plug in shower at the back. With this configuration, water is heated by the engine, the Eberspacher diesel heater, or if on electric hookup, there is a 1Kw immersion heater.