I 10/10 recommend Tim's Sprinter van rentals. I loved this as an alternative way to enjoy the island. The beds were comfortable and easily slept our four - a little tight, but fine for couples and for siblings (my teen daughters shared one and did fine). I loved not having to drag the girls out of bed to get out to our daily activities - they just woke up wherever we wanted to be every day.
We mostly parked overnight close to friends' homes or beaches with public showers and bathrooms, so we didn't need the sink or potty, but everything we did use worked great. We drained the solar battery a couple of times during nights following rainy days, but the backup battery was very well thought out and carried us over each time until the sun recharged the solar battery. We also used the backup battery pretty constantly for phone charging. We had the van for nine days and the backup battery was still around 25% when we returned the van.
The camp chairs and boogie boards were an unexpected pleasant surprise that got lots of use.