[rickst29]

Your long post contains several different scenarios. You seem to using only one battery at a time, for the purpose of "remote charging" the other. (In the Truck on day-trips, or in camp with "remote" Solar). In Camp, the TM runs with only 1/2 of the battery capacity which you built, and complicated swapping schemes become necessary.

Remote Solar certainly has advantages when you are camping under trees... but I wouldn't leave an $800 battery, or a $250 MPPT-with-Boost controller, out in the open unattended. In many campgrounds. You would be inviting them to disappear.
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I hope that you haven't already bought the battery boxes and high-current Anderson connectors, because I think that both batteries belong in the Trailer, where they can be used together. The Batteries AND a Converter can be stored under the street side dining bench, forward of the propane heater, using just one bigger "12VDC +" Battery Cable back to the Inverter and DC Distribution panel. You may continue to use the frame as the "12V Ground" connection, although it will (probably) need a much larger wire from the A-frame frame lug, up and into the storage compartment. Wire size depends on your NON-INVERTER 12V loads, and the maximum charging capability of your Power Converter. (BTW, you know that you'll need a new Power Converter, right?)

You probably do not need battery boxes - I don't use one with single my "bigger" battery. Since my Inverter blows hot air out a new vent (in the "inside" wall of the compartment, warming up feet under the table), the batteries might benefit when warming up at the end of a charge cycle.

It sounds like more than half of your "swapping" will be into the truck, to re-charge a low battery during day-trips. If you are doing frequent day trips, this saves some gas (in comparision to my in-camp idling). Both systems (your time-consuming swap scheme, and my 'Stockton Booster' scheme) max out at about 440 watts net into the batteries. But mine involves only 3 steps: (1) Connect Bargman Cable; (2) Turn on the SUV; (3) Flick the SUV 'zombie switch' to turn on the Bargman Voltage Boost.

In my SUV, the Boost Converter (under the hood) Converts from SUV Voltage (12-14.4V, usually around 13.5) up to 36V. To provide 475 Watts into my MMPT (~ 93% efficient), @ 36V, barely 13A is needed on the Bargman "Trailer Battery Charge" wire. No overheating, minimal Voltage drop -- it's super easy for the Bargman cable to handle that. This works great for me, and another TM Owner. I think that you should switch to our scheme, and double up the size of your TM battery bank.