Carb drip tray gasket or O'ring?

In the absence of any advice, I will install the O-ring in the inlet manifold groove to seal up against the drip tray, and a gasket between the drip tray and rubber carb flange which is opposite to how it is shown in the parts illustration (page 102) but logic says to put it the way I just mentioned due to no groove for the O-ring if installed as per illustration. I also haven't seen any reference to installing the drip tray in any of the maintenance or installation manuals.

I am thinking of putting a gasket with the O-ring as I am not convinced the drip tray will remain flat enough to seal with just the O-ring. I will have to give this some more thought though.