If you're driving an RV, I'm assuming you want to stay at an RV park?
That said, Gettysburg does have a few year-round RV facilities. KOA is open year round (though their pool is not), and I believe Round Top Campground is also open year-round. We passed both when traipsing around Gettysburg this past summer, and they looked fine, though we were staying in a local motel.
Donna