Most tiny houses have wood exteriors. I recommend using treated or naturally resistant woods (with tannin) and back priming all exterior wood (painting the back side and edges) before installation. Exposed wood takes a beating from the elements but the back sides can only be protected BEFORE installation. Paints with their solid pigments protect better but require a 3-5 year recoat. Stains are more flexible but need UV inhibitors. They last 5-7 years. Back priming and rigorous maintenance are the keys to a successful and attractive exterior skin for your tiny.