My partner and I visited the Big Island for 5 days and we absolutely loved our time living out of the van. The vehicle we ended up with was a Ford Transit, which was likely a bit more spacious than the listed Honda Element. Check-in was super easy, and Josh provided lots of great recommendations for places to snorkel, eat, and explore.
We did make camping reservations at parks around the island which ran us an additional $40/night, though we were never asked to provide any evidence of a permit and only saw a park attendant present 1 of the 5 nights. The van was well stocked with everything we needed to make the most of our time. Cooler, bedding, towels, lawn chairs, and cooking gear were all in good condition.
All in all, definitely a great way to make the most of a short amount of time on the island and we would do it all again in a heartbeat!