Downloading Custom Rooms, which Files need to be moved to Tray?

So, I'm downloading a room. If you're curious, it's Merman Simmer's underwater room. And I've been told that certain files need to be moved to the Tray folder, and then they will appear in my library.

So the folder with the room contains four files, a .room, two .rmi files, and one .trayitem. I moved all four of these to the tray folder last time, and it didn't work. Then there's a folder with a lot of .package build mode items. So what do I need to move to Tray? Am I doing something wrong? Can anyone help?