Mate ,
If you are going to do any serious cruising on the Aussie coast don't go getting rid of fuel tanks.
You can make water but you can't make diesel and we have a lot of areas where diesel is not available.
I have 3,000 lts on board Tidahapah and previously when I had the Fiat I also carried a 500 lt bladder on the back deck for long trips such as round trips to the swains and outer reef.
With the Gardner and extra solar panels I am using less fuel so don't require the bladder.
I installed a water maker some years ago and so decreased my water capacity by 1000 lts but I can now carry more beer and wine. (bottles, as I don't like cask crap)
mate just my thoughts after cruising the coast for the last 17 years.
Cheers
Benn