My comment is for the case in your post #13 where the EGC is disconnected from the truck outlet to prevent the neutral from being bonded to the EGC on both sides of the GFCI, which would then cause it to trip. But because this would be done to avoid switching the neutral, the neutral on the load side of a break in the cord will remain bonded to the GES. And so both the neutral and EGC going to the truck inverter would be disconnected, leaving only the hot lines connected. For simplicity, assume that the only load is between L1 and N. Then because the neutral to the inverter is open, there will be no current through this load and therefore no voltage across it, causing L1 at the inverter to be at 0V relative to ground. This will make the neutral of the inverter, and therefore the truck chassis to which it's bonded, be at 120V relative to ground.