I've found standing water in my combo assemblies on our new 2016 Sunseeker more than once, and decided it was time to deal with the problem before it became a safety issue and/or a water intrusion point in the coach wall.
I found a "new recall" thread in the Forester forums regarding Stop/Tail/Backup combo assemblies that I've been participating in. While this is the subject of a recall for certain issues, the recall apparently addresses a module under the coach that is connected to the lamp assemblies.
Two links: The recall thread:
My experience with the issues I found with my assemblies: