My first thought was re-using 1/1200, like the Amera island and harbour usually touted for Dystopian Wars.
Then I started searching for ACW/WBtS, and stumbled across Peter Pig's "Range 7" Riverine items. Forts, gun emplacements, and the like for river warfare. Some might be useful.
Off the top of my head, shooting from the hip, and any other bodily homilies I can dredge up, but I'll cogitate a bit more.
Doug