They tried resetting the original GFCI, as apparently one needs to use a screwdriver rather than a finger, 'cause it has to go in pretty far to reset. That didn't work. They replaced the GFCI, and that didn't help. They replaced the breaker, and that didn't help, either. So now they think they need to trace back all the wires and see what's shorting - a dead short, they call it. But as we will not be plugged in on our first trip, we'll wait till we get back to take it in for its diagnostic, and in the meantime see if anything else needs fixed at the same time.
This dealership is really cooperative and good. They're not looking to lay blame anywhere, just to find the problem and fix it. :-) As for battery, well, we have a solar thingie, and we can always plug into the truck if we need to. This trip, we won't be that far from civilization.