Three-season cottage insulation / Discussions

...cottage. If I use the cottage 3 seasons only is it better to lay plastic down and not close in the crawl space in? On the other hand if I used it some times in the winter should I close the crawl space in the best I can and use an exhaust fan with a humidstat control to create some negative pressure?   Anytime a wooden...

...cottage I would definitely include a vapour barrier. It will also act as an air barrier if you tape it well, so it will be more efficient and not feel as drafty. Unless you plan to have AC and keep it really cold in the summer then you should be good.