The Wiki entry[0] for the secure trucks reads like some kind of Tom Clancy fiction. They allegedly have automated weapons systems that will kill attackers even after all defenders become casualties.
My friend likely worked with the prior generation. They were unwilling to go into any sort of detail. they did say, you don't want to be any where near one if the operators think you shouldn't be there. Their phrase was something like "There are extensive anti personnel defenses".
You have to assume that such a truck is constantly "phoning home" and hopefully has some kind of asset tasked to watch it constantly. Maybe the process to get in involves authorization from "home base" in the form of that private key?
While I doubt that anything could stop a truly determined and well equipped adversary, I would frankly not be shocked if the whole thing was basically packed in claymores facing out, just for starters. You won't care in that extreme about compromising the physics package; you'll already be scrambling every resource including NEST to the site. You just want to buy time, and there are a lot of ways you could do that.
Hell, maybe they include an EPFCG... that would be really clever.