Rick is hauled out already I think
Either way it will not be a sustained cold
Yes, my boat is hauled out. If she were in the water I wouldn't be worried.
Remember that things are a little colder up here where I live than down in Maryland. Where the boat is, the current forecast for Tue-Thur next week shows high temps averaging 6°F above freezing, and low temps average 7°F below freezing. That three day stretch is sufficiently prolonged that I need to take it seriously.
I honestly don't know why people fear leaving heaters on their boats unattended. If your shore power system is done correctly and has appropriate breakers there is very very low risk of fire. Heaters are certified for use in residential dwellings. They have built in thermal safeties and do not get anywhere near hot enough to ignite anything. They are designed for long term use.
If anything I would be more concerned about running heat lamps on Jerry-rigged light fixtures. On those you have much greater risk of overheating due to poor bulb contacts, or poor wiring connections on the light fixture itself. Even then the risk is low.
Thinking rationally, I agree with everything you say here. However, there are some other considerations.
The boat club frowns on leaving electric hooked up overnight, but people do it. A couple of boats do it all winter long, though the word around the yard is that they're not leaving heaters on, just 120v bilge pumps and droplights in cold weather. (People generally don't talk about this much, and they clam up if you ask too many questions.) If I'm going to plug in, I want to minimize the wattage for a couple reasons. The electric plugs in the yard appear to be ganged in a way that multiple boats could run off the same circuit breaker. If we all hook up a space heater, someone could blow the circuit breaker for multiple boats. I'm going to be there late Friday doing the winterization, so I'll probably be the last one to leave and can try to be sure I'm by myself on a circuit.
I stopped off at Walmart tonight and found some 72 watt incandescent bulbs (my drop lights are rated for 75 watts), so those are one option at relatively low wattage. I also found a really nice little 250W ceramic heater with overheat protection and a fan that keeps the whole case cool. (Much lower wattage than the 600-900-1500 heater that I already have, and don't want to use.) I'd prefer not to use any space heater, but I may stick the new 250W one in the engine room while I'm working, assess how it's working while I'm on the boat (not too cold, not too hot), and make a decision whether to consider leaving it for Friday night. We'll see, maybe I can get the whole boat, including motor, done in one evening and then I don't have to worry about electric.
I actually have one of those. They're way way too hot, and IMO jury rigging a fan would be much less safe than a purpose-built space heater. But thanks for the suggestion, these things are always good food for thought.