It’s hard being a creature of habit. Dang, there was just water here a few days ago…
I’ve looked into solar water heaters for the Canadian fishing camp. There are some places that offer a DC heating element that retrofits an existing AC element in a standard electric water heater. The DC element can take power directly from solar panels and heat water with it during the high-sun times of the day and then store the hot water for later use. But unfortunately, that won’t work for a stock tank application that has to be kept warm all the time.