Unfortunately I cannot "plug" anything in for extended periods at the marina. Only when I'm there. But getting solar-powered air circulation seems like a good idea...
I topped up the fuel when winterising..., I'm assuming that I will not be able to use the diesel once the boat goes back in and will have to drain the diesel fuel tank (any thoughts?). (What does" polishing diesel" mean...I've seen that mentioned a few times). I'll look into the additives/treatments for storage of diesel.
But you are right, winter is only harmful if you have water stuck somewhere. A hot and humid Canadian summer can be worse, which is why we pulled almost everything that was not fiberglassed, glued, screwed etc off the boat and sitting in a separate (temperature and humidity controlled) storage.(It's actually amazing how much useless stuff a boat can hold!
I also have a copy of an issue of Sail magazine on Spring Commissioning from about 5-6 years ago
....I still remember one recommendation that I have implemented is the application of lemon oil!. It takes care of the mold and mildew and is good for wood as well as almost everything in the head.
If I'd had the skill, time and money I would have brought her down to Guyana! From my house I can see the Atlantic! There are rivers to sail up into. One in particular, the Essequibo looks just like the St-Lawrence and the Thousand Islands (well...close anyway). It was recently charted quite a ways up. It's also only a few days out of Trinidad or in the other direction sail down the Coast of Brazil...I'm going through withdrawal......