We have the Kenmore stackable washer & dryer too. We have not had any yellowing on the outside yet. It is vented too.
Also the Kenmore has a switch on it that will only allow you to wash or dry at one time. My husband (Don M) on here, He put another plug-in in basement and he added a cord and plug on the washer, (They were sharing one cord) He plugged the dryer in closet where they sit and the washer is plugged into the new plug-in, in the basement. Now I can wash and dry at same time.
If anyone is interested to know how he did this you can send him a private message. He will try to explain how he did this.