Hi! wow .a lot of questions.
wiring diagrams for camper converter I hope that helps some.
One thing you asked was
" Don't want this back feeding into truck batteries or via versa, right?"
That's right . So to avoid that you need to isolate the battery in your truck when the truck is off. there are several ways to do that but probably the simplest is to get a continuous duty solenoid from an RV or auto parts store, it looks like a starter solenoid, and run a wire from a hot when key is on source to it and a #8 or larger wire from your truck battery to the solenoid ans then to your camper battery.
Have fun