This is the layout with the full width rear bench and corner seat as pictured below.


As the storage area is lower I assume any water tank would be also, either stored under the corner seat (marked 11) or the usual place near the bulkhead under the bench (15).
I've seen two sizes on Ebay but not seen one fitted in a van yet to work out if/where.
Anyone got a picture/own a Joker 2 that could advise?