Jennifer Kelley of AB Lifestyles (800-825-4533) ...
... gave me a quote on 2-13-2019 of $79 plus shipping, if total order is less than $99. This would be a custom fitted bottom sheet and flat top sheet for a classic Winnebago Class C, with square corners. This quote was for a size of 60x96x5. You should measure your bunk first to assure that it is of the same dimensions.
My wife insisted upon making the sheets herself. It took her about 10 hours to do. If it were up to me, I would have just ordered them.