I have a 400 litre tank in my connect L2 Llimited,That's more than enough.,don't be fooled by the space on the back as it looks more from the outside,the bulkhead is almost half way the length of the van.
Good vans though but we find the Fiat Scudo more practical with two side loading doors and has more room, not too big or too small,just right for window cleaning.
theres plenty of room though.....
my 500L tank is fitted length ways inside a PURE FREEDOM frame so i have room down the sides and it evenly distributes the weight better so im not overloading either axles....
yes the bulkhead encroaches on the space a little but i still find i can store something in the "gap" at the base of the bulkhead(fold away step up).
i would have loved 2 sliding doors but i only have my 2 leisure batteries and a a little fold away trolley down the non door side......