" Don't want this back feeding into truck batteries or vice versa ,right ? "
Not necessarily . I use a lighted switch on the dash fed by an always hot wire to energize the solenoid . With the switch on and truck running it's charging both truck and TC battery . With switch on and plugged into shore power the converter is charging TC and truck battery . With switch on , not plugged in and truck not running you can gain some extra power to the truck or the camper depending on need . With the switch off truck and TC are isolated .
There are several good write-ups in the TC university on converter installation and truck charge wiring . Good luck