instead of experimenting with your generator ,go to any good generator shop ... ask them to refer you to a trusted sound proofing maker, they will make a whole box for it which prevent generator from dust/water and other stuff ...also it has vents for ventilation and a cabinet door so you operate generator easily.
secondly they will make exaust outlet themselves ...
the thing which venom has done is not appropriate as rain water will directly go in and will screw his generator soon.