If it's "wired-in", sometimes even "pros" get shocked by the current. If it's wired-in, my view is that it needs to be disconnected from supply and output to be safe.

The classic issue is that you show "no load" with the AC to the boat "off" -- then you assume the inverter isn't there; and, you become the "connection" as it suddenly connects through you or some device to ground.

You can also get some strange stray currents from some inverter wiring into the "ground" systems which suddenly isn't isolated between the AC and DC ground systems.