You could probably just ask; I do not think they would mind you coming in on a weekend or something.
Really, trespassing to make a film is only necessary if you are going to a WAR ZONE or something.
Asking is the worst thing you could do when making a film unless you have money.
It never ever ever works.
I've tried asking and it never worked.
I just went and shot and it always worked.
This case it's government property. Also doors are locked in the weekend. Remember it's summer session, no one is supposed to be here at all without permissino.
When school DOES start it'll be much easier because we'd just say we're film students.
I dunno if i'd get punished I am just very nervous about the possibilities because I am clueless.