Hi,
I used a 2 lug connector, and bolted this to my frame, then ran the 000 wire to this connector, then to the battery, so have the best of both worlds. When my motorhome engine is running, I can get about 100 amps from the alternator, and it will have a return path on the chassis frame, while not running the engine, the wire will go directly to the battery via low loss copper wire.
In your case, I would run the controller to your charger location, then #4 wire to the battery, there is no need for both the solar controller and charger to have separate wires to the battery. My guess is the charger is located near the fuse panel? You would also want #4 from the fuse panel to the charger/inverter, for the least amount of voltage drop, unless the fuse panel is already wired close to the battery via it's own large wire. Many times the factory wiring is pretty small.
If you will be installing 200+ watts of solar panels, then upgrading the truck to tow vehicle wiring is probably not needed. however if you really want to be able to recharge the trailer battery from the truck, then changing to #8 wire (or larger) with a isolator relay and quick connect 'anderson connector' would really make a big difference in the ability of the truck to recharge that large battery bank.
My solar system is 400 watts, and my RV uses about 35 AH daily to run just the refrigerator, CO and propane detectors. That is about what one 120 watt solar panel can produce in 1 day. Figure the amp rating on the panel times 5 hours, and you will get about the average solar production for one sunny day.
By the way, those batteries are about 75 pounds each, so you will be adding over 300 pounds to the hitch weight.
Fred.
