Yes he does! Hehehe! I went over that place I think 3 times. This SR is certainly not in a difficult spot. Oh well, at least I got it after opening only your first spoiler, lol.
If you haven't finished the Marsh yet, you can't get it. If you have, you now have access to a place near Loxton. Explore the outside of the buildings there.
I think that one is real sneaky! One thing I did notice, all the secret rooms are numbered in strict sequence, so you know that if you are missing a number it's somewhere you've already been.
If I can remember room 10 is off room 9 in the wastelands, room 18 is in the mines near the the room that the boulders keep falling please correct me if I am wrong