When concealed carry became legal in Wisconsin several other laws changed as well. The state DOJ put on training seminars for law enforcement regarding carry laws. I was at 2 of them. No less than the Attorney General and the Assistant Attorney General stated that non-licensed open carry in a vehicle is legal, and went through some scenarios as to what they would consider open carry in a vehicle.
This is not to say that some cowboy with a badge isn't going to going to try and nail you with CCW when your pistol was clearly visible on the dash. I'm only saying what the AG's office said what the law is. If you have a CCL you don't even have to worry about it. Eventually I hope we get constitutional carry and all these ridiculous rules and laws are tossed.