That's what I did. I didn't realize you mean the aluminum sign board. Go heavy on that caulking. I attached my flexibles to sign board with sikaflex, the edges didn't have enough are started to peel away. I had to tape over the solar panel edges to keep them from catching wind while driving.
I may slide through the south west, but If I do it will be winter. I hate the heat here in the Midwest let alone the desert in summer. Although, when its hot here, the humidity is usually darn near the same as the temperature..
