I wouldn't use Starboard simply because it is too difficult to glue together. If you wanted to go synthetic I'd use either PVC trim boards or synthetic decking like Trek, both are products from the housing market. Frankly, my boat is 34 years old and not one piece of window trim needed to be replaced when I removed all of them 3 years ago to replace window tracks and rebed to stop a couple leaks. That tells me there's really no good reason to deviate from the original fit out. Just my opinion of course!