My tip for the final battle.
When the patriots come along, make sure you are on the top platform. Get undertow, and drag them up. Drag and one melee shot and repeat. It will usually melee one off to drop to their death, and the other will remain motionless at the top. Go and kill all of the other enemies.
This method will allow you to defeat the wave of enemies, and give you an opportunity to scavenge ammo, set traps, and re-set your Return to Sender around the core. When you're ready, go up top and melee the Patriot to death.