pinchio-
Here is a link to the wiring diagrams for your coach:
Table of Contents
See sheet 1 of the
Body, 12V Wiring Diagram
for the BATTERY MODE solenoid that connects the chassis batteries and the house batteries. It's pretty simple; the battery banks are connected when:
1) you push the BATT BOOST switch, or
2) when the engine is running (if the BATT BOOST switch is in that position)
Nothing else... no special timing circuits, voltage threshold circuits, or the like. If the alternator voltage exceeds the voltage of the combined battery banks, then a charging current flows from the alternator, to the chassis batteries, through the BATTERY MODE solenoid to the house batteries.
You might want to look at this active thread, too:
Converting to Lithium house batteries