As absurd, unconstitutional and slanderous towards gun owners as 227d is, it's really quite simple about long gun transport.
You can have the ammo in the case or out of it, doesn't really matter, just can't be in the gun. I prefer my pocket, and failing that the case, but not seated in the receiver.
My suggestion is to leave the case with the rifle in the front seat, unless you are going within 1000 feet of a k-12 school, because at that point the treasonous federal gun free school zones act pretty much requires trunked transport. If no schools are in the area, and if rapid self defense or hunting firearm deployment is desired, this is the only way to transport your long guns. This allows deployment of a gun like an AR or other box magazine fed rifles in under 3 seconds. Beats the living hell out of having to go to the trunk.
"Broken down" is kind of a hard thing to explain, but at times I have taken this to mean that the bolt is removed, and have removed the bolt from a rifle or shotgun, then stuck it in the passenger seat while I drive to wherever I'm going. I generally don't like it, because having loose parts in a car has bad idea written all over it.
Funny how by law we have certain rights, but also by law we become crazed lunatics when we go to places of learning or get behind the wheels of multi ton killing machines.