So if you went to a single bank of Batt's would you run every thing to a bus bar and then feed the inverter and start circuit or would you run thru a relay to start the road engine ( and remove the isolator I take it). If you run to a bus bar would you place the 300amp fuse that is now in the system after the bus bar?
Don, you don't want any fuses in the alternator/starter/battery pathway. With a single bank, no bridge relay or isolator is required.
The way I would wire this is that the single battery bank would be wired to the alternator and starter exactly the way the OEM chassis batteries were, with a large switch to disconnect the alternator and starter from the batteries. The "house" system would connect to the batteries through a fuse of the appropriate size, just as if they were house-only batteries. So the inverter/charger and all house loads would be on the other side of that fuse from the batteries.
In this scheme, there are really only two connections to battery positive (one for the chassis disconnect and one for the house fuse) and two connections to the load side of the house fuse (inverter/charger and main DC panel) so there is not really a need for a buss bar.