You are right. They tow/impound the vehicle while waiting on a warrant. It used to be there had to be probable cause for a warrant, but once you refuse (if you have the parking decal) you give the probable cause.

Where I went to high school, it was not uncommon to see both a shotgun and a rifle in the back window of a truck (small town, and kids didn't understand things flying around in a crash). I doubt there was a car in the parking lot that didn't have some kind of a firearm in it.

Having said that, if one had any other contraband you darn well didn't park on campus.