This whole thing is about not having enough room on the tongue for two batteries. Solution is to:
A. Carry two 100ah AGMs inside the rig as some folks do--under the sofa up front is popular so you can drill a hole in the floor under the sofa and run wires down there and up to the tongue to connect the batteries.
B. Carry another battery or more in the truck and on arrival, put them on the ground next to the tongue and use jumper cables to connect to the one on the tongue.
C. Bring the generator to run the converter to recharge the batteries as required. You don't need to carry gas for it, since it has enough in it to do a couple of recharges and you are only off-grid a few days so that should be plenty of gas.
For this job, for A. I like the "12100" AGMs I have now in the truck camper. For B. you can't beat Sams or Costco 6s in the States for price. (You can jumper a pair of 6s with a 12 on the tongue for while camping and then at home put the 12 on the converter and the 6s on a separate maintainer.)
