You are correct and too badSeems pretty ridiculous to me and I'm not comfortable with that.
Anyhow, it has to be encased and unloaded in a vehicle.
There is some case law that implies that the gun case has to be out of reach. This is being debated on this forum as we speak.
So... The gymnastics to open carry in WI is as follows.
Put unloaded weapon in case. Put case in trunk. Drive. When you get to where you are going, pull case out of car, do not rest case on car while doing this, pull gun out of case, load and then put empty case back in car. If you open the case while it is in or touching the vehicle, you just violated WI concealed carry law.