Strictly speaking, you don't need to define treasure_room. You can use:
start_at = your_treasure_room
I've done it this way and it works fine.
And "imply_header_from_location_id = true" is optional. I don't use this, as my location ids are just room01, room02 and so on. I did it this way because I found that the location ids conflicted with the object ids when I wanted the location to be visible as scenery outside the location. (For example, I can see a barn when I'm outside the barn.) It also means that if I change the location name, I've only got to change it in one place.