The bridge is easier to cross on a vehicle than on foot, so you may want to mount up in the Mobile Unit spawn point inside your base. In fact, vehicles play a major role in controlling and winning this scenario.

Vehicles will likely take a lot of punishment from enemy Demolishers and turrets trying to cross the battlefield. Use the Demolisher's Arc Welders to repair damage to your turrets and vehicles, if time allows, but be careful: because fixing damage isn't easy in the middle of a firefight. Sky Jockeys are also equipped with Arc Welders, but they should concentrate on gaining air superiority with Steeds and transporting soldiers with Mules.