Mine went straight into my existing tank after i gave Neil the dimensions,your best bet to get the full benifit is to go for a flat tank covering most of the floor space,just tell Neil the make and model of your van and he will come up with the best option for you.Your looking at about £500 but it is really well worth the money and your van will drive completley different to the way it does now you wont know your carrying a lot of water even when full to the brim.You can choose where everything goes which is a real bonus as far as pumps outlets goes,he also allows spaces for DI vessels etc carved out in the tank.