Leaving Luggage in Car at Halemau’u Trailhead?

My partner and I are planning to backpack in Haleakala for 2 nights on our trip to Maui. We will be transitioning between hotels during the hike, so the plan was to leave non-hiking luggage in the car. Is it safe to leave our luggage in the car while we hike, or should we drop it in a secure location during the hike (like our next hotel, or luggage storage at the airport). Dropping it somewhere would mean either extra time on our drive that day or an extra expense, so would prefer to avoid if possible.