If you decide to winterize your water system, consider what I've done for 12 years to mine, also in Detroit. I added a T with a valve to the output of the water tank before the pump. In the fall, I drain the water tank and then hook a hose to the T and put the other end of the hose into a gallon of the pink antifreeze. Then turn on the pump and feed the pink stuff through the entire water system. What I've just done is to winterize the system without adding pink stuff to the water tank itself. Cleaning out the pink stuff from the water tank in the spring is a royal pain, but flushing the hoses isn't nearly so bad. The pint or 2 of water left in the tank won't hurt the water tank, it'll probably evaporate anyway.
You should plan on backup power systems for power outages if you do live aboard in the winter. I've read that shrink wrapping with the transparent stuff created a very good greenhouse effect. Sorry I can't help you further with your prep.