I agree with Executive.
What would happen if the OP was in a class B or C and went out for the day and didn't leave anything in the site to make it look like they are coming back. Does the camper telling the office they are leaving and canceling the rest trip, make it ok for the park to rent out that space for those unused nights? If giving a refund then yes. If not then no. I guess the moral of the story is to ask if you can get a refund and if they say no, then tell them never ins and then just leave. But it would be morally wrong to rent out that space when it's already paid for.