For those who actually care, i ended up doing some test with a spare tank we have and filled it up with water. We removed all the charcoal canister and pump lines and turned the tank upside down to see if we would get a leak through the vent line. We didn't get a single drop so the cut off valve really does it's job. To make sure we didn't get any fuel vapor coming inside the cabin we used the vent line that goes near the gas cap and connected both together. We are also eliminating the line that went to the front of the car.
here is a pic for further reference if someone ever has the need to do something like this.
