You have a fresh mortar next to you, as well as an ammo box near you and to the back. This battle gets pretty chaotic quickly. You can start off by using the mortar to bomb all the Drones, maybe even toss around your frags to see if you can hit that e-hole. A few may climb onto the back of the rig too, allowing a good chance to use the chainsaw. Don't forget about that ammo if you need it. And no turret for this fight.
Keep an ear out for when the enemy mortars appear, then use your mortar to blast them all away. Next comes a few Boomers, who can be made short work of with mortar rounds. Lastly will be two Reavers on the left and right, so hopefully have can finish them off with your last mortars, easy if you had some from the previous area and the one on this rig. If not, just take cover and use perfect reloads of the Lancer to carve up the beasts to end this act.