Yes it traps the gas efficiently buy the main issue is the unpleasant aspect. I kinda made it look decent with the use of some rubber bands, but really a picture would be needed, but unfortunately i only got the Sony Ericsson T630 camera phone that takes crappy pictures.
if you try to build one, be sure to tension the hose as it tends to curve under the pression of the gas underneath, but do not bend it too much. Also, at the end of the air tube that goes into the bell, be sure to add a seringe needle(but cut it's sharp tip cause the fish can be seriously stung) thus reducing the size of the bubbles because if the CO2 bubbles come out to powerfully they will disturb all the trapped gas, making it escape in a sudden burst. Even knoking on the aquarium wall is risky.
As for the decorations... i'm not sure it would work.
All the best, Liviu.