the cel is fuel safe's top of the line pro cel. It has a check valve built into the vent port already.
I have heard to put it under the car and then been told absolutely no because you will get dirt into the cel.
The vent allows air to escape with expansion and filling and air to enter as the fuel is consumed.
Since some fuel may be purged out the vent when it is topped off, I didn't like the idea of locating the vent near the fender which is very close to a red hot rotor. Then I was thinking about using the hole from the radio antennae but it is right in front of the driver's door, don't want fuel in there either.