Just now I am thinking of such a location. I am a frequent fuel and pit stop customer there, and I am trying to find the kindest way to inform them that the stalls are less than half the size they need to be in order for people not to pretzel themselves on the way in and out of the facilities. Meanwhile, you need to be careful!!! The spaces are small, and the main, swinging door does not lock. In this location, you need to stand with your back against the door and risk being hit and pushed by the swinging door. Or,you could stand near the hinges of the door and risk having your body gouged by the hinges from the swinging door (if someone enters while you are taking images). If you stand outside the door and balance on one leg while holding the door open with the other leg, you will be in a walkway and people might think you are a pervert for taking pictures of a restroom. They might just jostle you if they are in a hurry or oblivious. If that happens, you will just fall on your unprintable and that would be a big ol' PITA. *sigh*
This is probably the worst case scenario. Hopefully, your location will be different and it will be easier for you to obtain images discreetly.
Nature does not hurry, yet everything is accomplished. - Lao-Tzu