VikS,
I think you'll want to model the towed and motorized river barges that have navigated Europe's rivers for centuries. River and canal barges were also pressed into service by the warring nations as machine gun platforms, obstruction booms (at Zeebrugge), artillery platforms (outside of the ROF world though, along the Danube and in Mesopotamia), as troop ferries, and widely as hospital vessels.
Popular manufacturer's would be Freycinet and Luxemotor (our forum members in Europe might be able to find line drawings and more photos of the period's barges perhaps).
Here's a website with some brief history on France's barges:
http://www.riverdancebarge.com/history.htmlHere's photographs of WWI barges, showing how they looked, and a few showing details of barges converted as hospital transports (all open source):



