i set my bus up with a "floating" 12v house circuit. i do not use the bus body to ground it at all.
there are some advantages to have the systems separate, and some advantages having them tied together.
some of the comments are right on like you can't charge your house bank with the alternator. they'll need their own charger. on the plus side, it wouldn't drain your truck battery, no matter what. and its probably safer, if you're willing to run 2 wires everywhere.
safer because the 2 systems will not short out each other. i can take a hot wire from the house battery, and accidentally brush it against the body and nothing happens.
my battery charger for the house battery does ground to the chassis. but its only the 120v side that grounds, the output from the battery is "floating".