leave the 12v battery in place
When you have a built-in generator, you need to leave at least one 12v battery in place. That will ensure you have enough 12v power for generator start, jacks etc.
I presume the EG4 has a built-in charger and transfer switch. This allows you to wire the EG4 between the coach's built-in transfer switch and your circuit breaker panel. Therefore the EG4 will power your converter, which will keep your 12V battery charged.
Don't worry about trying to charge from the standard 7-way plug, you will get so little power compared to your large system that it is not worth the effort.
There are a thousand details that you have not made clear, but this is a general overview how to wire an all-in-one into an RV
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