This was a big job.
To summarise the steps:

1. Ran cable from main battery to auxiliary box
First there was the problem of getting the cable. I wanted thick cable as I want to be able to charge the main battery from the auxiliary, although this seems problematic. Even 20mm² was about $18 /m so as I needed about 5m that would be $180 for the positive and negative. The jumper leads I had recently purchased were about $100 and were supposedly 5m, but when I measured it was only 4.7m. This meant it would be tight. It was the best option and I ran it through the fire wall directly behind the main battery and then just behind the dash and under the from drivers step then under the floor to where the battery bank box was going.

2. Build a box to hold the batteries.
I made this out of plastic sheet 9 mm thick for base and lid and 12 mm for sides. It was glued together with Polyurethane solvent cement that I had used for the Icon Plastics siding and gutter. It was also screwed.

3. Mount the DC to DC MPT charger

4. Mount the AC to DC charger and distribution Panel.

5. Mount the Inverter

6. Mount Solar Panel on Roof

7. Install Circuit Breaker at Main Battery

8. Wire Everything Together