Looking at the OP's photo again, that tent camper trailer looks like something that would used in the outbacks of Australia, you know, one of those rugged off-road campers. If this is the case, then most likely it was custom built and attached to the side of the camper. Looking closer, you can see it's actually attached. Looks like it's got a spring loaded gas filled arm, and looks like the shower curtain may just fold up under the roof, the roof folds down on the side, probably has a snap catch of some type to keep it from flipping open when traveling.
If this be the case, this one was probably custom make. If so, one could be fabricated pretty simple with just a shower curtain and small shower basin, or low flat tub for the roof. Looking at it more with the suggestions above, it looks either home-made or custom made and attached to the camper. You may never find another one like it.