I can totally understand your concerns here, but I'm not going to forget to disconnect.

I'm talking about using it like three or four times a year, primarily for things like my upcoming pig butchering and hopefully deer processing. Flipping on the breaker and filling the tank, then shutting it down when I'm done will be no different than the same process I use at a friend's cabin.

The shop is too far from the house to reasonably use a frost-free from there, not to mention that forgetting to disconnect that hose would absolutely cause a problem if it's cold enough to freeze. A closed hose hooked to a frost free spigot will break that spigot like it had never heard the words "frost free". Ask me how I know that...

The water heater will be in a place where even if it did flood, there will be zero consequences. Also, I wouldn't even be planning to do this had I not found a working water heater for $25.