They need to be guarded whether they are officially open or not and in some cases need even more guards to keep people out now that they are closed.
Not really.
Sandy Hook there's one road on and one road off. And it's just "guarded" with a barrier and a cop who drives a roving patrol (I've snuck on at night, after hours, in order to fish). I'm sure there are Parks personnel out at the end where all the buildings and stuff are but I would suspect that with the shutdown it's just a skeleton crew. I never went out in that direction during non-business hours surreptitiously so I couldn't say. I've been out there after normal hours legally and I saw neither hide nor hair of any employees other than a Parks Police cop driving his usual patrol and the state Fish & Game warden.
Morristown is a collection of buildings in the center of town. They lock the buildings and it's otherwise patrolled by Morristown municipal police. I've worked there in the past and I know the current director/archivist.
So, they hardly need to call out the National Guard and turn these places into hard targets because of a shutdown.
Anyhow, aside from "civilian" guards and Parks Police, consider all of the administrative, maintenance, part-time staff (concessions, gift shops, book stores, etc..) curatorial, interpretive, and other "professional" employees. Not to mention the Rangers.
As with most endeavors that involve people carrying guns the tooth to tail ratio of guns to bean counters is usually very heavily skewed toward the bean counters (and other assorted non-armed, non-sworn employees). Since I can speak knowledgeably about Morristown, there are 2 full-time permanent Parks Police assigned, 12 other employees who work there full-time, and maybe a dozen part-time staff at any given time (not all working at once, but on-the-books doing shift work).
So you keep the two cops on the books, maybe add a third (though I doubt the necessity of it I'll accept the devil's advocate position that it's necessary) and lay off the other 23 employees.
Seems like a "win" to me if your source of funding is cut off and you need to pinch pennies.
Maybe you're correct about there needing to be more guards when it comes to some parks.
I don't really know.
The two that I have personal knowledge/experience of/with it certainly isn't the case, and as I've illustrated, even if they need to add a few more guards or pay their existing guard force some overtime they're still cutting out the great many salaries of the lion's share of the staff that have nothing to do with safety/security.
Look, I don't necessarily agree with what the Tea Party is doing in the House to cause this shutdown, but I think it's a legitimate and perfectly legal (though perhaps unconventional) tactic. I don't fault them for it.
But they're the ones responsible for our National Parks being shut down. They cut off the money and people don't work for free.
You can pretend that it's cool to run our National Parks system with a handful of guards and nobody else but I really just consider that to be dishonest turn-around nonsense.
You're the Party of personal responsibility, take responsibility for the fallout that results from your behavior.