When we first started RVing we planned to visit my sister and her family in MA. We had planned on camping at a park in Cape Cod during our visit. A few days before, the campground called to say a forecasted Hurricane was causing them to close. They offered us a credit for another visit or a refund. They storm never hit, but we still got our refund.
I definitely would have argued to get a refund in your situation, but my guess is they wouldn't have given a refund. Since the campground never closed, they'd argue it wasn't there fault you didn't stay there. If they cared about their customers, they should have at least offered you a partial refund. That is definitely a campground I would not return to.
-Michael