For camper sites you have to reserve them for atleast 2 nights. And you can make reservations the day before if you want, but the sooner the better if you'd like to get a good spot.
I would highly recommend calling the now if you already have a date. It is a popular park and it fills up quickly. Especially during the summer.
I believe the cabins fill up a year in advance so you might want to get them as early as possible. not sure on the camp sites but know they have certain # depending on power and they seem to be full when we go.
Long as you want
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