Follow-Up:
Mine came on several times while travelling on the highway over the course of a year. The mechanics used their computer handheld and each time said it was my gas cap. After buying a new one and making sure that I tightened the cap properly after each fueling, I discovered that the filler tube connection was not properly made and allowed a loss of vacumn that lighted the check engine light. Winnebago has to extend the filler tube when they convert the VW chassis for the Rialta. Have a mechanic check that connection and make sure it is secure, The check engine light has not relighted since I had it repaired. While changing the oil the filler tube may have been bumped and caused a vacumn leak.