So you want to infiltrate the Raider Fort?
Very well... but they won't just let you walk right in.
Raider outposts are places where you can obtain Raider Supplies, the Dungeon Key for the Raider Fort. To steal the Supplies you will have to kill the Raiders that spawn there. They spawn in groups of two about every two minutes. There are two different Outposts.
The Desert Outpost is located along Highway at 2620x 71y -780z. Located at 1585x 74y 1225z or along Highway "Three" is where you can find the second outpost, the Swamp Outpost.