The first thing I do when im nod is buy a flame trooper and run up the tunnel. Anyone comming down it meets a firey death. Since they cant see to shoot properly due to the flames, your shotgunner will be next to usless. Once I've done that I'd be off to buy a chem trooper with the cash I've earned and kill some more GDI. By the time thats happened a Tech will have been bought by someone else and the tunnel will be mined.(Hint: throw mines on the roof of the tunnels, with your back to the way the enemy will come down. If you do this in sloped, dark areas, the black back of the mine will be hard to see. BOOM. )