On my 1980 Hatteras 37 Convertible with twin DD 6-71s NAs I have just a copper or brass mesh in there that has oxidized and now drips that green stain that I hate so much. the way my vents are made there is no way for the spray to make it to the engine room unless the boat sinks so these mesh things are pretty useless and I will remove them all together. Maybe replace with 8x8 or 12x12 SS mesh just for the sake of itbut I do not see the need for it as we do not get the dirt and dust out at sea.