2 Battery banks built from 6 volts

Hi all, I did a quick search of the forum but couldn't find what I was looking for.

I have a 2018 17ft Jayco travel trailer. The majority of our camping is in the middle of nowhere. (boondocking) The trailer came with One 12 volt however, we swapped that out for two 6 volts from Costco.

We have One 100watt solar panel on the roof that charges the batteries through an 8 amp pwm charge controller. (plan on getting another 100watt panel this spring)

A 1000 watt inverter that is really only used to run a small tv/charge iPhones etc..

We have a 2000 watt Honda generator that we use to run the microwave and top up the batteries if needed.

I want to get another two 6 volt batteries however the space on the tongue is extremely limited. (can just fit the current batteries as it is) I do not want to store them inside due to the obvious hazard of that (and space is limited)

My thought is to install the 2 other 6 volts in the bed of my pick up, and have them as a separate second bank.

I have attached a rough drawing of our current electrical setup.

I know that if I do this I will need to use a battery selector switch and ample sized wire for to voltage drop.

Maybe I am over thinking this but exactly how would I wire this up?

My plan wouldn't be to run them on the 1+2 ever, but have the selector switch on 1 (batteries on tongue) and then when needed switch the selector to 2 which would be the batteries in my truck box.

Perhaps where I am getting hung up is how would they all charge? If the selector switch was selected to 2 (the batteries in the truck) and I fired up the generator, would that just charge those batteries? If the switch was on selector 1, would the generator just charge the trailer batteries?

How would I have it wired in order for the solar to charge the batteries?


I hope my question makes sense?

I have attached a picture at this link:
Click For Full-Size Image.

Please shed some light. Thanks so much,

Greg