You cannot sleep in your car at Arches National Park unless you have a reserved campsite at the Devils Garden Campground, which is the only designated campground within the park. Sleeping in your car outside of a designated campsite or parking area is not permitted. If you have a reservation at the campground, you can sleep in your car or RV as long as it fits within the boundaries of your campsite. To find more vehicle-friendly accommodations near Arches National Park, you can explore options on Hipcamp.