Put a custom made water tank (about 60 litre) in the spare wheel well with stainless steel pipe running through it. Connecting the outlet radiator hose to the S/S pipe running through the water tank and having the hose connected to the other side of S/S pipe carrying the coolant to the engine (as normal)
This would have the radiator return pipe heat up the shower/washing up water in the custom water tank.When you get to your destination you will have hot water in the custom tank for a shower etc.
You could plumb in a shower and water filler cap.
Cheers
Philippe