Civil War did have some trench warfare. Some of the old Civil War forts in Georgia had trenches as well as tunnels. A-lot of the time those tunnels would hold ammo caches and other artillery meant for the cannons that were posted on the hills. So while there was trench warfare there was also tunnel warfare.
Few years back I went on a tour of the Eastern parts of the U.S. and so I had the chance to see a-lot of the Civil War forts. Really amazing history.
As far as your map goes, it's very bland and basic. I'd definitely suggest working on adding variation to the terrain. You say you're lazy with terrain which makes the idea of making a Civil War TDM a little impractical considering a large chunk of the battles were away from forts and cities and were mainly in the wildlands. So as fun as the idea of a Civil War TDM goes, I don't think you should continue this project if you say you're lazy with terrain. Unless you plan to practice with terrain.
