Questions about 12VDC wiring

I just added 2 6v batteries to my camper for a total of 4.

I now have 2 banks of batteries, they will be hooked up to a selector switch which will allow me to run either bank or both together.

Here are my questions, 1) can I use the same wire to ground the banks to the body or should they have their own grounding bolt?

I also run a 1000W inverter, The positive wire will be connected to the common lug on the switch so that I can use it no matter which bank is in use. But what about the negative wire? can I jump the negative from both bank together? also can the negative from the inverter be grounded to the body or does it have to go to the battery?

Thanks for any input

Questions about 12VDC wiring