Head to the main train yard marked in the map to find the map. There are no enforcers you need to kill for this racket and the trainyard isn’t necessarily hard to secure. There are two entrances; one is through the main entrance and the other is through the basement entrance to the east. The basement entrance gives you easy access to a medicine cabinet and tac-vest so I recommend going through that route. After clearing the locker room, carefully go upstairs to reach the office.
Ignore the non-hostile workers in the office. There’s a sentry there as well as a roving guard so stealth kill both of them. There’s also a pile of cash in the main office and a Vargas painting on the wall. Head to the end of the office to find a stairwell that leads to the map along with other weapon & ammo crates that you can destroy to deal damage to this operation. Kill the lone guard there and steal the map. You can then proceed with destroying the weapon crates and escape / fight your way outside.
The guards are stretched thin so it shouldn’t be that hard getting stealth kills. There are three sentries; one for each entrance and the other is in the office area. Use the many covers to navigate away from the enemies eyes and don’t forget to lure them to you by whistling.
Don’t forget to loot the album cover in the trailer office outside and a Vargas painting in the office in the upper levels. Completing this objective will unlock two more objectives related to this, both leading to locations in the bayou.