There's a hole in their fence on the opposite side of their base perimeter from where the studio entrance is, there are a couple enemies here you can pick off relatively safely without alerting others and then you can sneak around behind some stacks of lumber. From there you should see a garage entrance on your right that has 2-3 enemies inside, don't go in there, instead stay crouched and go past the garages (note that there sometimes is one patrolling guard here so be mindful of their position, they do a loop in and out of the garage entrances). After the second garage entrance on your right is passed you should see a smaller dimly lit garage in front of you, that's where the intel is. Stay crouched and just make a beeline for it. It's about 50-50 if you get spotted here so prepare to hole up in there to fend a few off as they track you down. When the enemies stop coming grab the intel (don't forget the weapon recipe on the same table) and make your way out the same way you came in.
This is definitely one of the most difficult Tower cache areas to infiltrate due to sheer numbers of Tower soldiers though it ended up being one of the most satisfyingly tense sections in the whole game for me due to just how vigilant you have to be at every moment and make every shot count.
just finished this section myself and did pretty close to your spoiler tag, got back out and was taken down in the street, but at least that left my back pack with the quest item far enough away from the base to snag it quick and run back to the boat right as the bells rang