I think the Mar-K test confirms my own experience. There is no clear finish that will hold up to UV and the rain drying cycle. If you want to recoat every two years a clear coat will work or if you keep it garaged it will last. I am going to use latex paint but mine will be a daily driver in the northwest. I considered trying a penetrating urethane and putting it under a vacuum when it was applied but I still think it won't last. I have been a woodworker my whole life and have never seen a clear finish that will last without continous maintainance.