How to represent tunnel in CM design?

[Bear]

Suggestion:
Lay tunnel route with open ended factory feature. If vehicles can't pass through then a road boardered with tall pines will provide a canopy and simulate a tunnel.
Then stack opposite sides of the factory (tunnel) with the steepest elevation along the length of the tunnel.
That would insure no LOS or traffic from the left, right or above the tunnel. Unless some infantry manages to reach the summit and shoot down?