Not really. The beach park showers are cold water, used for rinsing off sand and salt from the body and water equipment. Most of them drain into the ocean so use of any soap, shampoo etc is frowned upon.
Not a great idea to do the Road to Hana the last day. There can be issues and road closures so it’s risky to get stuck. Plus leaving all your luggage and valuables in your car on the RTH can lead to disaster as well.
Why not reschedule that RTH day? I agree with TB4, not a good idea. Another reason not to do it on your last day after checkout is that all your belongings would likely be in your car. That isn’t safe. Break-inscan easily happen while you are happily splashing in a waterfall pool.
If you can’t book a late checkout, you could make that last day a resort spa day. Then you can safely check your luggage while you enjoy some luxury, and you come out clean and refreshed for the flight home.
If that’s not your style, maybe a day at Haleakala summit and/or Upcountry where it’s cooler. You won’t be swimming, so wouldn’t need the shower. You’d still need to deal with the luggage, but you could lock it in the trunk if you travel light.Edited: 21 February 2018, 00:08