Actually, it does say the bit about plugging in to cool the battery in the manual. Haven't tested if it actually does for lack of appropriate weather here in the Northeast.
True, keeping the battery at 100% is not ideal, but overheating it is significantly worse. If I could choose between the two, I'd keep it cool.
Keep in mind that the car doesn't float the battery continuously like a lot of consumer electronics do, but turns the charger off completely once that battery is full, and doesn't turn it on again until charge has dropped a few % points. I suspect during the OP's two months it won't be that often. I occasionally park mine for a week when I'm traveling, and it never enables the charger again during that time. But I haven't had the patience to leave it until it does to see how long that takes. I just can't be without my smart for that long!
Come to think of it, except for the potential heat issue, 2 months is a really short time, so it doesn't really matter what the charge is.