If it were me...
I've always gone with the theory that if it doesn't have water in it, it can freeze. I would drain the block - that is not that hard to do. Then proceed on from there. Disconnect the hose running from the T-stat housing to the water pump. Then disconnect and dump any other lines from the t-stat that have low points that water would settle in. Disconnect the line running to the raw water pump. Disconnect the hose going to the oil cooler. Bump the starter a couple of times and you will get some more water out.
If you have a heater and shower, you need to disconnect those lines and blow the water out. Since they are small lines and small units, they would freeze first. A light bulb in the engine compartment is not going to help the heater core that is up front. The heater is a pain to get all the water out because the hoses to/from it have low spots in the middle of the boat. If you blow air through you will at least get the water out of the heater core and that should be sufficient. I like to dump a little pink AF down the hose and blow it through the heater core just to be safe.
I'd spend the time getting all the water out of it. Running it today or in two weeks from now will not matter much at all.
If that boat is outside tonight, add windchill to the temp.