Transit CUSTOM conversions
Just for info , and please check if this is correct before buying - - -
27 L Fresh Water tank from CAK will apparently fit in the void in the van wall behind the driver's seat EBAY item https://www.ebay.co.uk/itm/272930188780 Filling is done from outside the van but as it is inside the van (and insulated) it should not ice up in freezing conditions
CAK can weld connectors (40mm, 25mm, 15mm and 10mm) onto this tank according to your requirements. They also supply a universal mounting kit EBay item https://www.ebay.co.uk/itm/272818998621.