We just throw a foam topper on our rear corner bed. The foam topper is inside a removal (zipper all around three of the four sides) cover that can easily be removed for washing. The corner bed's mattress is covered by a nice color-coordinated bedspread furnished by Winnebago that we have never had to wash or change over the years. Making up only the foam topper couldn't be easier - just a sheet and blanket thrown over it when not in use.
By the way, a rear corner bed is the only way to get a nearly full-sized queen bed that is permanently available at floor level in a 24 foot non-slide Class C motorhome. We use both the rear corner queen sized bed and the overhead cab queen sized bed - both are comfortable. The overhead cab bed is the most difficult to make up of the two.