I lived in Annapolis, Maryland for a few years. Conditions there are a bit
worse than yours. We got 4-6" of ice on the bay's creeks in some years. The
low temps were roughly equal to yours.

There are several issues with leaving a boat in the water:

1. Freezing of the surrounding water and the grinding that can occur on your
external hull. Sounds like this is not an issue for you.

2. Freezing of the throughulls in more severe climates. Also not an issue
for you.

3. Freezing of the raw water and fresh water system. This can and will
happen to you. You can either drain or purge the raw water system with
propylene glycol antifreeze. Do the same with the fresh water system. It
shouldn't take more than an hour and 5 gallons of PG antifreeze to do both.
You should temporarily install a bypass around your hot water heater so you
don't have to fill it with antifreeze. Drain it instead.

You can keep electric heat inside your boat. But then you are vulnerable to
a power failure which is more likely during a cold snap. Unless you plan to
use your boat during the winter, I would antifreeze it.

David