Base Assault focuses on the Engineer being able to effectively aid in the assault on an enemy owned territory and the base or outpost there. Engineers are primarily a support class so this loadout focuses around that aspect.
Engineers should focus on supporting their team during Base Assaults. Keeping all your teammates and vehicles fully repaired and stocked with ammunition will be vital in keeping the assault at full force. Defenders have the advantage when assaults begin by being able to spawn continuously at that base, while attackers have to either have a mobile spawn point or travel from a nearby owned facility. By keeping all vehicles repaired and in the fight, the Engineer saves his/her team time and resources.
Nano Armor Kit - This is how the Engineer class repairs vehicles, MAXes and other equipment, which the one important ability the Engineer can bring to an assault.
Mana Turret - Good ability to use to support choke points when no one requires repair or assistance. Especially good at keeping enemies locked inside spawn locations while your team takes control of the base.
Ammunition Package - Allows your teammates to replenish their ammo constantly while assaulting the enemies base, very useful for assaults.