I tried looking for the law, but haven't figured out Michigans law stuff yet, but I believe, (someone correct me if I'm wrong), that added that you could carry a pistol, locked, in a trunk, for "all lawful purposes", or something to that effect.
But, I never really worried about it since I've always had a small game license (carrying to or from an area open to hunting), and am surrounded by forest that is open to target shooting. If I would have ever gotten stopped, you can bet that I was going target shooting, or hunting, if they would have asked. But that was before this law went into effect. Now I have my CPL so it doesn't matter....well, it does, but you get the point.