defender shower

hi,

i'm in the middle of overlanding up my 90 for a morrocco trip and am hell bent on putting a shower in, i'v got a shower mixer from whale and the pump etc, i just need a way of storing water, i want a permanant tank underneath some where, i'm thinking under the drivers seat, any one got any ideas, i can't find one for a 90 anywhere!!

Ta Matt

i've seen this on my friend's landy, a 30litre water bag which sits ontop of the sloping part of the roof, above the driver and passenger.