Follow-Up:
Probably a fuse. The location of the fuse could depend on the year of Rialta that you own, as VW sometimes rearranges the fuses from year to year. You definitely won't find anything on this in your Winnebago manual, but you should be able to find which fuse to check in your VW Eurovan manual. The fuses are usually located under the dash on the left side of the steering wheel. Since both of your windows are affected, I would assume it's something central like a fuse instead of a burned out motor since that would be very coincidental for both motors to burn out at the same time. If you don't have a VW manual, post a reply and I'll look and see what fuse it is in my manual for my 2000 Rialta.
Here is a link that might be useful: MotorHomepage Rialta Resource