Head for the trailhead Campgrounds in eastern side of Pawnee to begin this mission. No matter what vehicle you arrived in I suggest you grab the nearby motorbike for its great handling and best off-roading ability.
For the most part you can stick to the main roads of Pawnee during the tail. When needed, you should try some off-roading in the hills to allow you to take major shortcuts and make up any distance. Eventually the helicopter will stop and hover over the Pawnee Trailer Park and your objective will update.
Note: By now I am going to assume you have at least one Spec-Ops weapon and will be doing most of your assaults with stealth via the silencer. This means that I will not longer be offering melee stealth paths or aggressive paths with standard firearms. I will, however, offer alternate paths if there is a way to complete a mission without the means of a weapon.
The Trailer Park has many access points, militia, as well as the helicopter blocking your progress through the camp. The best insertion point is on the west side of the restricted zone, up a path behind the drained pool. Since you need to go in undetected until you spot both security chiefs you should hack the helicopter camera for a better view of the area.
With this view you can scout the area by Aiden, which has one militia member on the ground to the north and another on top of two trailers connected by a walkway, where there is also an Audio File: Maurice Vega 05 . With the chopper locate the two security chiefs: one near Aiden’s position to the left of the connected trailers and another at the back of the park to the south of two Enforcers.
You can now head through the area with either force or stealth, but I suggest you use stealth, with a Spec-Ops weapon, and stay in cover so that the helicopter doesn’t spot you and notify the ground enemies.
Start with the closest security chief, who can be taken down when the helicopter is out of view and the militia on the roof is walking away. This will give you a new checkpoint that is great to start at if you are killed or want to return to a stealth run. Once the first chief is down, headshot the sniper on the roof and melee combat the militia to the south by returning to the small road and working your way behind him.
Once these three enemies are dead you can make your way south around the area, waiting for the helicopter to pass when needed, and then stop at the van near the entrance to the final chief. Wait for both the Enforcers to head down the path and out into the trailer park before sneaking in behind them and quickly taking down the chief.
Once both of the security chiefs are down you can either escape or finish off the militia to complete the mission.