Depending on how your inverter works, and how your trailer is wired, a subpanel may not be that much extra work.
It was super easy in my KZ. The shore cord was connected directly to the WFCO panel, via a 30a breaker. I simply undid that connection and installed the smallest panel I could find, which was two slots and four circuits. I put it right behind the wfco (lots of wasted space behind the converter inside the cabinet). Two new pieces of 10/2 romex were installed, one from the shore power panel, one from the WFCO panel. These go into the inverter transfer switch.
The inverter output connects to the same breaker the shore cable used to, and the input is connected to a new 30 amp breaker installed in the shore power panel.