I can see the need for a 30a switch if one of the sources is shore power 30a while the other is 15a from inverter. The OP was intending swapping between Honda 2000 gen and 2000w inverter, where each has only 15a.
How would you set-up using a transfer switch where you first choose to plug into your inverter (no shore power) and then want to plug into gen, where the gen is not built in, but is outside somewhere and does not have a remote start?
You have to go out there to start the gen anyway, so what is extra hard about unplugging from the inverter and plugging into the gen while you area at it?
In fact, with no auto transfer switch you can have both sources if desired, with shore cord into one and an extension cord from the other source powering something detached from whole house:
EG -plug-in type converter to gen maxing out the gen, while still being able to run other 120v loads off inverter instead of having to wait till the battery is charged up so there is enough room now on the gen to run other 120 loads
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