The laws governing the transporting of firearms in Iowa are constantly changing. Below are the applicable laws in the State of Iowa as of February 11, 2015. The below information is designed to be a guide and not the final word. If you have specific questions, please refer to the Iowa State Police Web Site. Another great resource is the Iowa Gun Owners, a non-partisan group dedicated to preserving the gun rights of Iowans.

With a valid Iowa permit or out of state permit the State of Iowa honors: You may carry a loaded handgun, rifle or shotgun in a motor vehicle; however this does not apply to snowmobiles or all-terrain vehicles (see Iowa Department of Natural Resources:  Iowa Hunting Laws and Weapons Permit Applicability)

Legally Transporting Handguns, Rifles and Shotguns in Motor Vehicles Without a Permit to Carry

You may still transport firearms in Iowa without a permit under existing Iowa and federal law. Under Iowa Code §724.4, you can either carry or transport an unloaded pistol or revolver in a vehicle inside a closed and fastened container or securely wrapped package which is too large to be concealed on the person, or you can transport an unloaded pistol or revolver inside a cargo or luggage compartment where it will not be readily accessible to any person riding in the vehicle. In other words, if you have a cargo or luggage compartment which is not accessible by anyone in the vehicle, such as a trunk, the handgun simply has to be unloaded.

Iowa Code:
724.4 Carrying weapons.
f.  A person who for any lawful purpose carries or transports an unloaded pistol or revolver in a vehicle inside a closed and fastened container or securely wrapped package which is too large to be concealed on the person or inside a cargo or luggage compartment where the pistol or revolver will not be readily accessible to any person riding in the vehicle or common carrier. 

483A.36 Manner of conveyance. 
No person, except as permitted by law, shall have or carry a gun in or on a vehicle on a public highway, unless the gun is taken down or totally contained in a securely fastened case, and its barrels and magazines are unloaded.

When a motor home is being used as a means of transportation, a permit to carry is not needed in a container or if the weapon is unloaded and package too large to be concealed on a person or inside a cargo or luggage compartment where the handgun is not readily accessible to any person in the vehicle. When a motor home is used as a residence place of business, no permit is required.