mounted a pad-eye in the ceiling for any future failure. Be prepared,
the boy scouts say.
Unable to find a replacement 20-gallon tank in a pinch, I decided to test the limits and try an 11-gallon model from Kuuma. So far so good, but I'm not sure back-to-back showers are possible, but the recovery time is very short.
The pump was not so much of a surprise, but unlike the water heater, it had increased in price about 50% to near $400. I'm not sure why it didn't occur to me earlier, but I still had the Shurflo 120V RV pump (only $110) that I'd used to cobble together a water system in the trailer. I'd already ordered a replacement Grunfos MQ, but I decided to plumb-in the Shurflo as a backup.
I made up a sign describing the now 3 modes of operation and the correct
valve position for each: Normal (Grundfos), backup (Shurflo), gravity.