Yes, USRanger does have an approved terrain for Special Arenas called Twinrvr. It is not listed on the download link from the home page, but MrMidi, Soda or USRanger could tell you where to get download it. The map includes custom made destructible bridgess, and clouds are made to look like sandstorms.
There have been some terrains that have been updated also, but terrains for the MAs are much more finicky. But in as much as I hate to agree that even some newer MA maps that I love the way they look and feel, but are a real drags to play because of the horde or nothing fights that occur on them.