Still not clear if you have an "inverter", or meant "converter."
If you do intend to run some 120v things from inverter and the rest of the rig straight from batteries when off grid, there is another way not yet mentioned.
You can have your 2000w inverter inside the rig on a couple of AGMs (two 100w deep cycle ones is good for that-- can run the microwave and toaster and kettle and TV/DVD etc) You plug the shore power cable into the inverter and shut off your converter--run the fridge and WH on gas (do not put the fridge on "auto" or it will go to 120v, not gas)
Leave two Wet cell (two 6s is very good for that) on the tongue for normal 12v usage.
So now you have two separate systems. You can use a portable charger run from the gen to keep both sets of batteries up as needed (will likely be on different days before each reaches 50% and needs a "50-90" recharge.)
You can also have two sets of solar, one for each set of batteries. Or if your solar is portable, you can swap over between battery sets using the clamps on the battery posts, whichever needs it first .
You can get Eg, a 25 ft jumper cable set up to #1 AWG cu-al not too expensive, (unlike the cu ones) and just jumper both sets of batteries and use one charger and do them all, then return to two separate sets
Or you could set up one in the truck bed like you said and use jumper cables.
You can cart along extra batteries and set them on the ground beside the tongue battery set, jumper them all up, and then when leaving, tuck all that away and head on to the next campground.
You can do whatever works best for you! Almost anything will work, and no doubt somebody else has already tried it. You do not have to re-invent the wheel to go RVing! Glen Curtis had some good ideas that still apply :)
