There's a road very close to the campsites. You can drive down to unload and then park your car at the welcome station (3-5 min walk away).
You can park 300 ft from the site and pack it in. Or, ask the host, and he'll let you drive up and off load. I live there on the Island and that's how we do it. All the best and enjoy.
You could also bike or walk from the ferry terminal. It is quite close.
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