There are definitely dry basements in Maine. There are definitely wet basements in Maine. All depends on where the house was built and/or how well the drainage is. As far as humidity, Maine probably isn't as humid as SE US. We had a couple of weeks of 80%+ humidity this past summer. I think average humidity in the summer is closer to the mid 60%. I would still use the golden rod in the safe. Depending on the home you get, the dehumidifier might not be necessary. I think heated basements are not the norm. Boilers/furnaces are usually in the basement and provide some heat. Many basements that are not finished will not have any other heat. In my last house, I had forced-air heat. There were a couple of outlets in ducts in the basement, but I had one closed.
Where in Maine will you be?