I'd recommend going to the East side of the compound, run along the fence and there is an opening. From there head towards in between the guard tower and the South part of the compound. Then use diversion grenades to sneak into the main building.
I actually did this on the Community Hangouts stream 2 months ago, based on advice from community members (since this was my first time completing the mission). Feel free to check out the exact location and how we did it here - https://www.twitch.tv/videos/406058438?t=01h34m13s