>We have a storage off our deck and keep a generator there. It has gas in it and it has been treated with that stuff to help make it more stable over time. Regardless, I have been instructed to create a small vent in the door to allow vapors to escape. All that said, and knowing that gas fumes tend to hover around the ground, my question is, should the vent be put near the top of the door or the bottom. Does it matter?

Why not put vents top and bottom?
I invested in solar panels and made a power generating windmill - (no gas:)
You can find out how to do that here: http://www.otherpower.com