thanks prater

does it need to be vented like the ones with the filter on top or just a tank?? thanks

It needs to be vented. I am actually thinking of removing the filters off the top and connecting them to a blower with some ducting. That way the fumes from the engine are expelled straight out of the engine compartment.

hmm I dont like fumes, I guess I could run a tube to the blower hose and just attatch it to the blower hose somehow???? so when the blower is on it sucks out the fumes???

That's why I mention running the hose from the catch tank back to the carb. The majority of residue should be caught in the tank, and there'll be just enough vacuum near the carb to provide a suction.
The only negatives I see tying into a blower are that you need to run the blower when you're running the engine (if you want any vacuum), and if residue happens to make it through the can, it coats the blower. My guess is a flame arrestor removes/cleans/replaces easier than a blower.
You could also add a through-hull type fitting (bilge outlet, fuel vent) somewhere near the air intake/exhaust vents, protected from any water, and vent to the atmosphere. I noticed on my 311, even though the blowers are on the starboard side, they cut holes in the same area on the port side. FWIW.

It is just a thought on using a bilge blower to evac the slight smell of engine oil. I was thinking along the lines of an ebay special for $20.

would this also work, mybe better/worse than a catch can?
http://www.jegs.com/webapp/wcs/store...63433_-1_10449

I hvee installed PCV valves in all my boats. Ususlly in the rear behind the carb through the intake into the engine lifter valley and a breather in the front of each valve cover.