The best Stronghold I found to easily get this achievement was the "Hinkin Factory" in the Lombard Red Zone.
First I recommended that you use the crossbow, distractions and RC car bombs.
Once you have completed your preparations, there is a small opening between the fortress and a nearby building where you can use the RC cars to eliminate as many enemies as possible.
Then use one last Hack Car to openning the gates of the Stronghold and carefully proceed with the crossbow.
If the minimap flashes red during a takedown of an enemy, that doesn't void the achievement, but getting the red detection meter filled will void the achievement.
Once you have killed every enemy in the base, deactivate the valve and you should get the achievement.
BUG NOTE: It is possible that more enemies could spawn in the stronghold while you deactivate the valve, screwing you over. It is also possible that enemies can spawn outside the base and somehow see you through walls.
(Video below in Portuguese, but You can see the strategy used)