The most technical but fool proof way is with a sub panel
Circuits you want to power get moved to the sub panel
A transfer switch goes between the sub panel and the main panel and the inverter
The transfer switch , changes between main panel or inverter
When using Shore lower or generator
Power flows main panel -ts -sub panel
When there is no external power shore or genset
Power flows inverter -ts -sub panel
This costs the most
But is totally automatic
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A manual switch inside is no different than using the shore cord plugged into the inverter
You have to remember to turn off certain items, run then on l.p.
Etc..