Although the other solution helps with the majority of levels. I don't think it is true of this one as at the end when making a run for the helicopter, there doesn't seem to be a spawn limit. It is more a case of you have to clear out the right side and make a run for it. Here's a video which helped me quite a bit:
*Note when he's gone around the truck right at the very back and says run forwards, I recommend running and diving behind the cover where Connor is just incase as I ran straight into the yard the 1st time, came up objective completed but then was shot in the back.
**edit most people believe this vid was not in fact filmed on guerilla difficulty, I have left it in as it still highlights the tactic required.