Charger

https://www.ebay.com.au/itm/PROJECTA-IDC25-12-VOLT-DC-TO-DC-25A-BATTERY-CHARGER-SOLAR-VERSION-4-CARAVAN-AGM/302957268505?epid=24008806292&hash=item4689a90e19:g:MbYAAOSwOGFcyud-&frcectupt=true

This does both Alternator charging while the car is running and solar to your auxiliary battery.

Only problem is it doesn’t have a good readout of whats happening so you have no idea if the solar is doing anything.

This unit it much better but $$ (my brother just put it in his car)

https://www.ebay.com.au/itm/Enerdrive-DC2DC-Plus-40A-Battery-Charger-EN3DC40/254178856509?hash=item3b2e3d8e3d:g:988AAOSwG8Zcmv~y

Or you could put a dc monitor on it for about $50

Solar panel, flexable mono panel, you can get bigger if you want, basically what ever will fit on the car. The projector will do upto about 400W, the enerdrice will do up to 800W

https://www.ebay.com.au/itm/200W-12V-Flexible-Solar-Panel-Waterproof-Caravan-Camping-Power-Mono-Charging-Kit/272893011251?epid=26026728309&hash=item3f89b0e533:g:HHkAAOSwt2FcrUPW&frcectupt=true

Aux battery, I put the 170AH slim battery in mine, but anything they want. 90AH will run a fridge for 3 days as long as the weather isn’t crazy. The chargers above will do everythin except lithium. But no one can afford lithium.

https://www.australiandirect.com.au/batteries/agm/?gclid=EAIaIQobChMI457wyMeN4gIVwRuPCh1ATAYLEAAYASABEgLtV_D_BwE

Fuse everything, cables from main battery to charger and solar inputs and then everything coming out of the aux battery. You don’t want a fire in the desert!

I used a mixure of ANL fuses and blade fuses

Jaycar has everything you need.

https://www.jaycar.com.au/search?text=ANL+&CSRFToken=d8a181a3-3f1f-4cf2-be25-8210152c3c51

https://www.jaycar.com.au/standard-duty-30a-blade-fuse-holder/p/SZ2040

https://www.jaycar.com.au/modular-design-blade-fuse-block/p/SZ2013