Here is something else to consider. The charcoal cannister. It would be another system to hook up, but it does not reduce the power output of the engine. The engine does purge any vapors from it, and recycles then back into the engines intake manifold, and the engines computer, with the O2 sensor reduces the amount of time the injectors are "on" because of the gas vapors coming out of the cannister.
I think is is better to gain the slight mileage, from having a sealed fuel tank, than just to dump the vapors out into the air.