Might be a slight advantage of keeping it filled insofar as corrosion protection, but not really worth the effort for 5 months.  It it was me, I'd leave it dry, making sure I put a note on the start switch indicating this.

I am just going to ask the question;
What about the block? Also the water heater, shouldn't they be drained as well?

I'm with Gary on this one.  I've never found it possible to drain ALL of the engine and connected systems. If the old antifreeze was not up to par, then the residual pockets of it will not be, either.  I would fill it with fresh antifreeze now, and not worry about it over the winter. My $0.02.

There are a lot of nooks and crannies inside the engine where a little amount of pooled frozen water can do a lot of damage. The benefit of the pink stuff is that it doesn't freeze hard. 

The Walmart in Ashland has -50 for around three bucks. The Napa has -100 for Napa type prices. It's worth it to buy a few of the cheap ones. -50 is really all you're going to really need. Even on the solid freeze two and three years ago -50 didn't happen, and the coldest Wisconsin has ever seen in it's history was -55, and you'll never see that in the lake basin because of the insulating effect in winter from Superior. Your engine has the advantage of the insulating layers of air pockets inside the cover, inside the cabin, inside the engine compartment. 

It's worth it to spend the time and the nine bucks for a few gallons. Run some through the bilge pumps, water pumps, and the head as well. And AC or hot water heater pump if you have it. 

If you don't have a winter cover yet, Ship Shape out of Duluth does good work and they are out our way often. Shrink wrap in Bayfield runs around $750, Ship Shape does a nice canvas cover that will last at least ten years for around $2300. 

Was a bad year for me, where I fell behind on a long overdue change of the fresh water cooling system. Seems my fuel pump went unexpectedly, by the time the replacement arrived where I could move to the in water storage marina, the dock water had been shut off. This coupled with the sudden cold snap in the North East US, led me to get resourceful (half ass) in winterizing.
  We have all discussed the problems with burping and fully draining a Universal 25. I drained 3 quarts of water from the starboard petcock, which is about half of the total cooling system, of 5 quarts plus the hot water heater loop. I then refilled with water from my own tanks. Ran the engine to mix it all well and drained again, then added fresh water again. In affect by now I had a highly diluted cooling system, or nearly all fresh water. Drained 3 quarts again and refilled with 3 quarts full strength anti freeze. After again running to mix it well, I came back a week later to find I am good to 4 degrees Fahrenheit. This is what my system has been at for the last four years, so I should be good. No fuss, no burping,no mess.

Jerry, I would like to make a few very important comments regarding the Antifreeze replacement.  First, never use the cheap antifreeze " pink stuff " in the Engine.  That stuff is for the water tanks, holding tanks, and bilge pumps, etc.  Always use the " True Antifreeze " used in All Cars.  Cost more like $12.00 dollars a gallon.  Secondly, never use " Tap " water,  Tap water has minerals that could eventually clog your water system.  Always use " Distilled " water.  A 50/50 mix is usually OK.  I sometimes use 60/40, slightly more Antifreeze which lowers the temp. even more.  Never use just " Antifreeze."  And you should not leave the Engine dry, " True Antifreeze " prevents Rust.