I keep hearing you talk about mice. I have had my lawn tractor almost chewed up by a rat or rats. I live in the country and I parked it in a small shed that was just big enough for the tractor. I figured this was surely better than having it set out in the weather. They chewed all the rubber from the steering wheel. There was nothing left except the little metal rod in the middle that looked like a steering wheel. They also chewed up all of the wiring. A couple of years later I got a new JD and I parked it outside in the weather for 3 seasons. It certainly never hurt it sitting out. If I were you, I would just expose it to the weather. That's what I did. I'm just too scared of rodents chewing on it. If you cover it, they will come. They like a nice warm dry place.

I'm sorry I don't know the answer to your question. Perhaps you meant to post this in the tractor forum? This a garden travelers forum.

Also it doesn't matter if code now requires decking as all that matter is what was required of code when it was built/installed so checking with your building inspector's office wouldn't do you much good. I disagree. The building inspector's office can tell the OP if roof sheathing was or was not required when the house was constructed. Some jurisdictions do require it with all roofs. The OP is in a hurricane area. Things tend to stricter there. It is possible, although unlikely, that the house may be required to brought up to current code (if it doesn't meet it now) upon transfer of title -- emphasize unlikely. The building inspector is there and should be on top of this stuff. Why discourage the OP from contacting him?

The previous owner of our home enclosed a side porch. The porch stands on stone piers raising is about 20" off the ground. They added a layer of foam sheet insulation under the floor. I know because I had to go under there and reattach some of it. I think the better solution would be to add a layer of wood sheet product, maybe exterior grade plywood, under the insulation making an insulation sandwich. It is still the coldest room in the house but the raised ceiling isn't insulated either. Just something to consider.