I have found that a "FOR SALE" sign will fix a multitude of evils.
Close it up and just tell the new owner that it needs a new battery.
But if you are too stubborn to quit, here is some help (maybe).
On my '61 Safari the wires in the battery box are:
Red #1---- 12 volts to everything 12 volt
inside the trailer
Red #2---- 12 volts to the breakaway switch and to/from the TV plug
for charging trailer battery from the TV.
As per previous advice, fuse all three.
I traced the green ground to an access panel on the front wall at floor level inside the trailer. There I improved the ground connection and added 4 more ground connections to the trailer body. A bad ground can cause all sorts of "weird" electrical problems.
As for your other ratsnest, I cannot say it any better than the "Lewster".
If I were you I would try it. It may work. If it does, redo all the connections and clean it up.