I saw many joints that probably should have been sealed with silicon caulk. That stuff would leak huge with a driving rain or a homeowner armed with a garden hose. Siding shouldn't rely on underlayment. Granted, I don't have "The sheet of Instructions" that come with the product, but you should be a little more forthcoming about the amount of silicon caulking it would take for a proper exterior application. Remember, think like a rain drop!

How do u install on concrete stucco foundation of house 4 ft high