I love it when this mission comes up. This is probably the most profitable L3 mission with 25m+ in loot and it actually puts a strain on my DNI tank.
The trick I have found is to set my default “keep at range” distance to around 72km, lock up the closest heavy missile battery, and burn out of range of the missile batteries while pummeling the ships giving chase. Once out of range I drop my MTU and orbit it at 2500m to make my boat a bit harder to hit and pound the incoming waves with T2 Hams. Once all the hostile ships are down and salvaged, lock up the Ore Processing structure, send in the drones and start hitting it with missiles once it is range. Finally, take out the two transports leaving the missile batteries intact.
Reason for doing the mission like this is if one destroys the batteries it incurs a -0.24 Gallente faction standing penalty whereas if just the ships are killed its only a neglible -0.003 standing loss.