We measured soil conductivity as well, which confirmed that the dunes behave as a relatively poor conductor.
Fortunately, MMANA applies these ground properties by default.    

The first step was making an electrical connection to the bunker rebar, which has a top area of is about 15 by 30 meter.

Here is Ed is welding a "ground rod" to the rebar.

   

Ground resistance was measured. It proved to be relatively low, which is good.

As a first test, a single vertical wire of about 18m was connected. On the first CQ on 80m the RBN reported 8 dB S/N in Australia.

Next, we worked VK0EK on 80m almost immediately.A video of this QSO is on line. The TL tube clearly shows the antenna current - proving that this current also flows into the rebar.

 

    Here is a view of how it will look in the near future.

A choice was made for a square 4-wire cage type radiator of about 16.5 x 0.5m, plus a top load akin the famous Radio Veronica ship.
As radiation resistance is low (about 10 Ohms), the currents are relatively high (design is up to 10 A). To cope with skin effect, the wires etc. must be relatively thick.