Thanks for the insight! It's a shame playing around with CSGTerrain took up so much time. I haven't tried that plugin, but making smooth terrain with CSGs seems like a real pain. That beach looks nice for something that was built in only a few hours!
I've only used Func_Godot+Trenchbroom and Blender before. I'm definitely gonna have to give Terrain3D a look, for when I inevitably want to mess with something that Trenchboom can't handle.