This one is the best choice for a "30 Amp" trailmanor:
https://www.bestconverter.com/PD-510...010Q_p_28.html
It contains two switches, one for the alternative "hot" wires and the other for the corresponding current carrying "neutral" wires. The output goes to the WFCO 30A AC circuit breaker.
There are two input wire sets. In normal (off) position, the transfer switch should connect the TM "30A" 120v power cord wires (from the grid, or from a campground power pole).
When power becomes present on alternate leads (your Inverter), the switches change position at the same time- first disconnecting from "the grid", and then connecting your Inverter (with a momentary disconnected state in between those two connected states)
This does not assure that the Inverter gets turned off, but it DOES assure that the grid connections will never be active at the same time.
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You will also need separate switch (or dedicated circuit breaker) to prevent the power converter from trying to charge the batteries from Inverter power, in an inefficient "loop" from energy being created by the Inverter.