Tom, if you're curious, Iowa Code 724.xx defines these circumstances. 357 is exactly right, you cannot transport a firearm in your vehicle in Iowa unless you have an Iowa CCW permit, or the gun is disassembled, or unloaded and kept in a secure container too large to conceal on the person and in the furthest extent of the vehicle. It cannot be accessible to any occupant.
Loaded mags may be considered 'loaded weapons', depending on who you ask. the latest word from DPS is 'no', but that changes like the weather.