2002 Harmony Water Tank

Hi
I have a 2002 Harmony, based on a 1999 Peugeot Boxer, somewhat modified over the years by previous owners. The current fresh water tank is approximately 50mm (2") deep, x 1200 long by 800 wide, and is slung around half way across its length underneath. The shallowness of the tank causes problems with supply to the pump. Can anyone tell me where and what shape the original tank was? I think I can see pipes hanging down near the back of the van, close to the waste water tank. Wondering if can move outlet pipe of existing tank to underneath (currently at side) or thinking of replacing the tank as fed up with not getting water, just mostly air, through taps unless sitting on a downward facing slope. If so, should I replace to where it was, or replace shallow tank with similar size but deeper one have seen online. Any info /thoughts appreciated. Thanks, Pat