OK. Finally got some time to update progress.
Ended up selling my in dash unit to a friend and buying one that fitted the space properly and kept the steering wheel controls. It isn't as user friendly as the old one but I'll look into that later.
Also got the electrical system mostly in as per this diagram. Still need to conect up the relay to cut out power to the front when ignition is off.
And got the tank in
The pump is connected so it can pump into or out of the tank or bypass the pump to fill from a garden hose. It's fitted to the side of the drawers but shown here before it went in.
And the Drawers
There's also the power shower under the bonnet.