Could always use field tower class for the tunnel objects that push the player's team in the direction towards his/her base and has no effect on the ai team.
Its not just the tunnel, a player can easily just drive over the hill to the other side of the map, if you do, you get a warning and 2 minutes to get back (too long). This is fine, a mission fail for disobeying is ok.
The first problem is what happens when you drive through the tunnel too soon, too many triggers go off at once and several voice overs get queued up making no sense at all.
The 2nd is... destroy the rec before it deploys, find the sensor thing and get back to base = mission complete in a matter of minutes without any significant opposition or any need to build more than a few turrets. Maybe this is how it was supposed to be but its not very entertaining.
The 3rd problem is that the deployed scion rec did not build anything, I am quite sure that it should/did do.