This was probably our favorite campground in a state park on Maui. We camped in a campervan, and there's a separate section for RV/campervans and tents. Campervans park in a mostly dirt (so it does get a bit muddy when it rains) lot adjacent to the bathrooms/beach shower and the grassy area for tent camping. The black sand beach is small and has rough waves but it is absolutely beautiful, and there's an incredibly lava tube (a cave, basically) that you'll have to do a little searching for (when you walk down the stairs that lead to the beach, look to your right when you get to the bottom and search along the rocks for an opening. You'll have to duck in, but once in the lava tube opens up far above your head and leads to an opening that touches the ocean).
You *definitely* need to get a reservation ahead of time for the park - it's easy to reserve online, but you must do it as soon as possible and print out your reservation to show once you're camping - they do have people come around and check.
The campsite for campervans has no picnic tables and just one old grill made out of bricks that looked a bit gross, but there's picnic tables near the parking lot where day visitors park, and near the trail along the coastline. There's a bathroom building at the center of the campground that includes separate women's & men's rooms with running water toilets (2 stalls in the women's), a changing area (basically just a bench) and 1 sink (with no soap or mirror). Outside of the restroom are soda machines and an open-air shower. The shower has multiple showerheads so 2-3 people can shower at a time, but they're all connected to one main rod so it is a bit awkward to be showering so close to strangers. During the day, day visitors use it a lot to shower off after the beach, but once evening comes around we saw a lot of campers use it just like a regular shower, just keeping bathing suits on. Considering the other state parks on Maui (like Kipahulu) even the beach shower was pretty nice to have to be able to shower off. There's also a water fountain next to the bathrooms and another very low-to-the-ground water faucet that many use to wash their pots and pans, and we used to fill up a large water jug.
The beach was great, as were the hikes along lava rocks - though they were definitely not super well maintained, and at times you were kind of guessing whether you were still on the same path. Overall a great place to camp!