Waverley Amateur Radio Society have produced a kit that helps to meet the need. As can be seen, it has six 12volt powerpole outlets and three high current USB ports. The kit was reasonably straightforward to assemble and I can recommend it to you. This along with my existing setup should be sufficient for the trip.
To follow the planned road trip check VK8MT-15 on aprs.fi. We are aiming to head off in a few weeks time.