The trouble will be condensation. The metal trim that surrounds your portlights now, has a thermal connection to the exterior. At night when the temperature drops or on cool rainy days, that metal will transmit the cool temperature to the inside ring and condensate moisture from the boat's interior. Just this past weekend, I was amazed at the moisture this thermocouple produced on Sea Gypsy (hull # 743). Just keep this fact of meteorology in mind when choosing a trim. :-)