Follow-Up:
I don't think there are any tailored seat covers since they are a Winnebago product and not a VW one. Your best bet would be to call Winnebago Customer Support -- they can get you exact match material for your seats that could be taken to an upholstery (sp?) shop to get the seats completely re-done or create seat-covers for you.
Here is a link that might be useful: MotorHomepage Rialta Resource