Bring back-up with you and go the back way into the command post with the ship. This will also work if you play as the Empire. You can see almost every turret on the map and get a good number of kills. Use the ramp to climb up on top of command post and get situated. Play as the rebels, choose a sniper and spawn at the command post with the ship.The Detpacks will make short work of the turrets, as well. It would be preferable to have the Engineer be equipped with the Award Shotgun so that enemies will be killed fairly quickly. You can also use the Engineer unit to destroy these turrets. If you don't destroy these turrets, they will rapidly decrease your troop levels.
Now, alternate between picking off enemies with your pistol, which will raise your rank for 'Gunslinger', and providing heavy supporting fire for friendly assaults by following groups of friendlies and blowing up turrets. It's probably a good idea to get some AI to come along with you (for protection). Then run along the walls of the buildings.
