Top down driving through the desert may suit the faint of heart just fine, but not the fair of skin. The rules of the road for convertible travel are similar to those for a hike in the Galapagos, starting with sun protection. Our everyday routine begins when we lather up every exposed area of arm, face, ear, neck, and leg with sunscreen. You could tell how out of practice I was the morning after day one, after we had wound our way over mostly rural roads from San Francisco to Bakersfield: I had failed to adequately coat the back of my hands, and an area at the base of my thumb, along with a tiny strip of my wrist where I wear my watch, was lobster red.
Proper hat selection is also key. A broad-brimmed model may be fine for protecting the back of your neck as well as your face when you're walking a wildlife trail, but in the Miata you'd have to lock it down with bungee cords to protect it from being carried away by the constant buffeting of the wind. A baseball cap is the only viable alternative. Even that has to be pulled low over the eyes to keep it on, especially when there's a strong crosswind across the highway.
Another similarity to a hike: the need to pack plenty of water. Dehydration happens almost as fast when you're sitting in a bucket seat at 60 MPH as it does walking down a dusty trail.
Then there's the packing. For this trip, the nearly-unused custom luggage we bought a couple years ago from a Miata parts web site finally came in handy on this journey. It's a four-piece set designed to fit into every corner of the miniscule Miata trunk, plus a long, narrow bag designed to fit on the deck behind the seats. My knapsack-style camera bag substitutes for one of the smaller bags in the trunk without destroying the symmetry of how they fit together, and we've squeezed our travel toiletries kit and one or two other small items into the slivers of remaining space.