if the gun is locked and the ammo is separate, then you are fine.
just remember, SUV trunks (or whatever you call them) are not the same as car trunks. (even if you have one of those plastic things that go over the trunk, so people cant see indie)
see, if you keep your gun in the trunk (in a car) then you can lock the trunk and its the same as a locked case. But that doesnt work with SUVs, because you can still have access to the gun. the key, is to not be able to have access to the gun while driving.
if you keep them on the back seat, then you need a case that is locked.