Can you build an onduline shed around it - tannalised wood, onduline,
fake window, fake door?
Essentially the inflatable tanks in reverse, unless some regulations
prohibit it.

Is it possible to bury a bunded tank, concrete lintels and slabs on
top?

If a tank is 1000L I can see someday it being worth £1k if not more,
black gold sitting in the garden as it were.