G'day. Looking good!
One tip - in one of your previous posts you talked about the white ants (termites) eating a pallet on the ground.
I suggest you treat your tank pads with Termidore and then put a layer of Cracker Dust on top of the sand to stop the little buggers eating the poly tanks.
Yes, they actually do! We lost 12,000 litres last year - one small hole in the bottom that we could not see.

If you're worried about using a chemical then put a sheet of Termimesh on each pad (maybe a bit more expensive)