The space is very narrow, however as shown in my draft drawing, the water line will comfortably sit above the peak of the centre well. I am not sure how much space I will allow for extra storage in the top half, but considering the space is narrow I want to dedicate as much space as possible for tank volume. I may extend the height of my tank from what is depicted in my drawing (haven't finalised this as yet).
Anyway I have started the base mould using layered high density insulation foam from Bunnings. Made a couple of templates from cardboard, bolted together and cut around with my home made hotwire cutter. Which is pathetic

I made the stupid mistake of applying bog filler directly on the foam causing a little bit of meltage. But have since fibre-glassed with one layer of 200g and I will then skim the surface with fairing compound... prime and the base mold is ready.
So here are some pics thus far. I hope to update as I go along. Hope you enjoy.