We arrived at dusk and were unsure whether it would be open as the website says the park closes at dusk but doesn't specify a time. Fortunately there was a machine where we could buy our camping pass and the gates were open (park wardens checked our pass in the morning).
We stayed in a tent so the windy road wasn't such an issue with our 4wd and there was one RV in the camp but I would imagine the 5 mile into the park would be slow going in an RV due to the windy road and low hanging trees.
It was totally worth the drive off the beaten path, there were only 3 others camping, the facilities were great (showers + flush toilets) and each campsite has a fire pit and picnic table and are nested under trees with lots of wildlife around and a nearby stream providing a serene setting.