12v dual battery setup - wiring, grounding and busbars
I think you try to connect your solar system to the car battery via the second charger. This is not necessary and will not work (Or has your van 24V?). You can just use a relay do disconnect the car battery from the others (for starting etc..). There are special relays for that on the market. You can search for battery disconnect relay.
Wiring the negative poles together is correct. Remember that in the car the chasis is used for negative potential.
The Ground connection of your Inverter should be grounded correctly. So you can wire it to a metal pole, take a hammer and push it into the earth or if you want to connect it to your chassis (12V negativ) you should ground your chasis (metal pole :)
Btw. most people don't wire the gorund connection of their inverter. If you only use devices without metal case/ground connection this should be no problem. But be aware this isn't correct.
Hope this helps you a little bit.