I would not want to get caught with an unloaded and cased handgun sitting next to me on the car seat. Under applicable law you could be charged with CCW. Of course, it could also be the ordinance (non-criminal) improper transport of firearm (suppose to be in the trunk or out of passenger compartment) -- but that's up to the arresting officer and prosecutor.
I would not, repeat NOT, advise doing this (or getting caught for doing this). Even though the AG's office may have conceded this is not CCW in the Gonzalez oral argument, no cop or prosecutor is bound by that argument alone.
Correct way to transport a firearm in WI: Unloaded, in proper case, and stored in trunk or out of passenger compartment if SUV (make sure it's not within arms reach).
Do I agree that this comports with our RKBA? Well, that doesn't matter at zero-dark-thirty when you're pulled over with your kids leaving on a family trip....
The two cases that will decide this in WI are Cole and Hamden. I recently read Hamden's briefs and filinig. He is represented by a very high profile large law firm. Unforturately they might be able "win" the case for him without any meaningful improvement for us.
Incidentally, Hamden operates a store in the most violent community in WI and keeps firearms for his and his family's safety. There have been numerous armed robberies and even one homicide in his store in the past decade. In fact, Hamden himself shot and killed an armed robber in '97 IIRC. Not only did he not get charged (self-defense), but he got his gun back. When he found out at a charging conference that he was getting charged with CCW in the current case, he asked the Asst. DA what he was suppose to do. The ADA said "Move to Brookfield" (an affluent suburb).
Have a nice day.