Our 2010 WGO Vista 30W Class A had the exact same problem. If you're handy with a few handtools, it's an easy fix. I, on the other hand, am not handy so I took it to a local cabinet maker whose grand son takes on odd jobs.
He glued & screwed 3 strips of wood under the drawer running from front to back. He also attached the front and back to the drawer bottom using small wooden cleats. The drawer is now completely rigid and works well.
WGO was in cost control mode in 2009 & 2010 so things like this drawer often got short shrift.
2010 WGO Vista 30W, 1993 Geo Tracker
Just a user with no RV or mechanical expertise