This is a CAD sketch of what each 2' x 4' trench section is going to look like from above. Each trench will be about 30mm deep; the fire-steps will be about 15mm deep. The circles are going to be used for gun (MG, mortar) emplacements or forward positions.
The circles on the side are the standard base sizes, for perspective.
I figure it will look a bit more curved and natural when I build it, but for now I'm trying to get the proportions down before I start cutting wood and foam. This is a compromise between a real trench and one that will fit based miniatures.