One way to approach it is this:
If you have a 200 amp service now from the utility, and you truly do want no change in capacity when the power is out, then you need a gneset with 44kw capacity (220v * 200a).
But that’s awfully big....
The only reason you you would have a 200 amp service is if you have an electric stove, clothes dryer and water heater.
Many services are 100 amp, and most could run on 50 amp.
Getting a generator of more than 5 or 6 KW starts to be expensive.
Generac does not have a very good reputation in motor homes.
I know someone who repairs motor home generators and he says most he repairs are Generac.