There are advantages and disadvantages to any RV electrical design. For the two inverter design:
1. House battery is always charged with a 3 stage charger (bulk, absorb, float) with the correct charge profile for your house battery.
2. Two batteries of different size, type, make, age, mfg. or mfg. date are not connected together for charging.
3. The house electrical is not connected to the vehicle electrical.
4. 120 volt AC is available with engine running for heating water or heating air or charging.
5. The vehicle inverter limits the maximum load on the alternator.
6. The house 12 volt system does not need to be grounded to the chassis.
7. Does not require a large cable between the house battery and vehicle battery.
8. Does not require a relay connecting the house and vehicle batteries.
9. 120 volt power is available at all the duplex outlets with engine running and with the house inverter off. (If you have an inverter with a transfer switch)
1. Can not use a switch to connect house battery to vehicle battery in case vehicle battery will not start the engine.
2. The vehicle inverter limits the load on the alternator. You can only charge at the maximum output of the vehicle inverter.
3. Slightly higher cost.
4. Not what everyone else does.
5. Requires two inverters.
Block diagram of my system:
Instead of relays I use three manual selector switches to direct the power to the function that I want to use. The normal setting is to direct the power to the house inverter/charger/transfer switch. The third selector switch was added to allow me to heat shower water with the house battery if weather conditions permit. If I know I will have unsed power available from the solar panel, I can use the houise battery for heating water.
The charging function using the vehicle inverter is a back up system only used if weather conditions force its use. Last year of Sprinter ownership did not require either shore power or vehicle inverter "shore power". All house battery charging was done with the 205 watt solar panel.
In Transit I have a 300 watt panel, Morningstar MPPT solar controller, Magnum MMS1012 inverter/charger/transfer switch and a 255 amp-hr. 8D AGM house battery.
Now back to comments about the "modified" Orton charging system. The diagram is not clear enough for me to clearly read on my computer. But is looks like you are using multiple relays to either use vehicle 12 volt power or power from the house battery to operate one inverter. This can be done with a simple battery selector switch. Select either of the two 12 volt sources to power the inverter. I looked at doing this but it ended up more complicated and not as fexible as the two inverter design.
An example using one inverter:
Using the three relays and the wiring gets the cost closer to the two inverter system.
The slight extra cost of the two inverter system eliminates a costly hot water system or allows air heating. So net cost is less than the traditional RV design of connecting two different batteries together for charging.
This system is practical for a small RV that does not require massive amounts of power from the alternator. For my application it works well.