My teen had a very, very challenging year due to some challenging health issues; he loves nature, swimming, and camping, so I decided after finding cheap tickets, to whisk him away for a week on Maui, someplace we've both been before and loved.
The van, as many have noted is a beast, in the best of ways, and although older, really has power and gets you where you want to go (barring a couple of places). Not necessarily the smoothest ride, but whatever. The pillows are great and the mattress very comfortable, though might be less comfortable for taller folks (we're both under 5'5"). We brought a couple of car curtains we have from camping, and that helped get it a bit darker and more private.
The sink worked great for quick clean-ups; we didn't ever use the portable showers as there are so many beaches with showers.
We like to cook and planned to do the majority of our meals while traipsing about; I think perhaps most folks don't generally cook as much, and I had expected more in terms of the supplies provided. We went ahead and bought a small frying pan to use in addition to the small saucepan provided. There was a good cutting board provided, lots of knives for cutting, spatula, stirring spoons...but then we were only given 8 paper plates, 10 plastic knives, 4 plastic forks, and 2 plastic spoons for actual eating. I'd packed our backpacking dish sets so it wasn't a big deal, just seemed odd. We also had just 3 bags for the camper toilet to last 6 nights, which was a bit challenging, but we made it work.
Other thing to note: the butane burner works great, just a regular Coleman single burner. The cans for these last anywhere from 1.5-3 hours depending on how high of heat. Through a mishap, we started our trip with just one, and it ends up that these cans are sometimes not too easy to find on the island. We checked 4 stores in Kahului, and were told they run out as soon as they come in. We found this out too late in the day and had to rearrange plans last minute and missed seeing Haleakalā, as the food we had bought required fuel to cook. We finally were able to track down a can back in Kihei a day later, and ultimately it was not a huge deal (just a bummer to lose our summit reservation), but a cautionary tale for other's who plan on relying on fuel.
Gas is also quite pricey...cheapest places are Costco and Safeway in Kahului.
There are plenty of places to pull over and camp for the night, though the west side of the island seems a bit more amenable to folks van-camping. Also definitely recommend finding a new place BEFORE it gets dark, lol. The first couple of days there we were having so much fun during the day that we'd let the day get away from us before realizing it, and then be driving around in the dark looking for what seemed a good spot. Definitely less stressful searching out places when you can see :)
All in all, it was very fun, and a great way to get away from the crowds and be able to see the island affordably. Also definitely appreciated the camp chairs, beach towels and umbrella.