As we only stopped twice drivin through Iowa (I didn't slow down driving until I got to Nebraska where I began taking breaks for Bogota and I's sake.) Cenex was a nice stop as it had a large lot for the semi's that were filling up at the diesel station right next to the regular gas station.
With all this lane, and the large lots of grass in front of the motel that sits there (if you'd want to rest) your dog can run around there as well, with a good distance away from the cars and trucks that are filling up on gas.
A nice gas station to stop at when you are driving through the midwest, and if you want to get gas before hitting Nebraska I would recommend this spot.
