A roll over valve is designed to stop liquid spills, not vapor. filters will stop particles from entering, but will not stop vapors from leaving. A bulk head fitting designed with a seal would work well. You absolutly need something. Random engine stoppage and a collapsed tank can ruin your day.
Something like this maybe with a nut on the inside
Holley Performance Products -6 AN Male to 1/2"-20 O-ring Port*985065ERL or a
Russell #670850. you can add a AN to pipe adaptor if you want to use plain hose with a barb fitting.