Battery charging
There should be no problem in what you want to do as I know of no converter that is not protected from reverse current. This is pretty easy to do as all that they need is a bolocking diode in the output. The reason that they have it is due to the fact that all modern RVs have the ability to charge the house batteries from the tow vehicle or the chassis. That supply will range up to 1V above the converter voltage so it has to be protected.