Lisa's initial theory was that the ground lead (line from the negative terminal of the battery to the frame of the vehicle) was loose or frayed. However, the screws were tight and wiggling the line did nothing, so she tried a different theory, this time with what looks like success.
The round thing in the center of this photo with two screws sticking out of it and one red wire leading from it is a Klixon CDLA-80 circuit breaker. Normally there are two lines running in/out of it, but we'd already removed the RV battery and the power feed from it to the breaker. This is an 80 A DC circuit breaker that stands between the coach battery and the coach itself. (That is consistent with the fuses back in the coach: 4 x 15 A + 1 x 20 A.) When Lisa tapped on the box, the lights flickered, and if she tapped harder, they went off entirely, then came back on when she tapped some more. Removing the breaker, she could hear bits rattling inside, which is probably Not Good.
To our surprise, we found the necessary part — what appears to be an exact match of the same part from the same US manufacturer, not a cheap Chinese rip-off — and we ordered it. As you'll see if you go look at the link, it's not even a very expensive part. Had our need been more urgent, we might have gone to Reno to the RV parts store, as there's a good chance they might have had one there; however, it will be some time before we need to take the RV out again.
Had we worked this out while I was on the road, and had we realized that just lubricating the hood latch would have made it open without assistance, I might have been able to work around this problem by just tapping on the balky breaker when I needed power. However, I survived (albeit with some accumulated fatigue from insufficient restful sleep), and for less than $20 in parts, we should be good to go once the replacement arrives.