gas fume venting-

I have decided to move my gas tank to the bow of the boat. This will put it under the deck-it's a 6 gal tank,I am wondering how to vent this area so the fumes can escape? for instance how big of a hole would I need? could rod holders with the bottom cut out be enough?Please let me know pics are welcome!

My tank is in my front compartment, on the top I have to standard inlets, https://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=112458&catalogId=10001&langId=-1&storeId=11151&storeNum=50667&subdeptNum=50677&classNum=50678#.UGOh_DvnEjA these face forward and force air in when under power.

For an outlet I have on of these on the back of the hatch https://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=18978&catalogId=10001&langId=-1&storeId=11151&storeNum=50667&subdeptNum=50677&classNum=50678#.UGOiZjvnEjA this seems to work fine as I never smell fumes when I open the hatch. I also have a 6 gal portable tank.

Thanks!!