Carb drip tray gasket or O'ring?

Does anyone have experience with fitting the Rotax drip trays. The manual shows a gasket between the manifold and drip tray then an O'ring between the drip tray and the rubber flange. The O'ring doesn't have a groove there so I think they have it pictured backwards and the O'ring should be between the manifold and drip tray and then the gasket. Or is it better to just have a gasket either side of the drip tray? 

I am concerned that the drip trays might not stay flat enough for the O'ring to seal.

What way have others done this and did any method produce a vacuum leak?