Experience now says that most gas fume issues are related to fuel leaks. Check all the fuel connections very carefully - the fuel rail connections, the fuel pressure regulator, all lines and the fuel injector seals. At least one person even reported a bad seal at the fuel pump (under the cargo floor area). If you don't see anything wrong with the engine not running, try checking everything again with the engine idling. The fuel pump will not run unless the engine is actually turning, which means that in order to check the system when it's fully pressurized, the engine will need to be running.
Oil leaks can also generate fumes, and oil leaks around the turbo or exhaust manifold can lead to fires, so pay attention to oil leaks as well.
Vapor recovery system
I no longer feel that the vapor recovery system is a factor in most fume problems, but it may be worth checking.
A line runs from the gas tank to a charcoal canister located in front of the right wheel well. When the engine is running, any fumes from the tank are vented into the activated charcoal, which absorbs the fumes. The bottom of the canister is open to the atmosphere. When the engine is shut off, a valve on top of the canister opens to allow fumes to enter the intake manifold. When the engine is started, the fumes are burned.
If gas fumes are detected in the passenger compartment, first check all fuel lines and connections for any leakage. Carefully check the injectors and their seals too. Check the seal around the fuel pump, under the cargo floor. Check the connections at the fuel filter (passenger side, just ahead of the rear wheel, underneath).
Make sure the hoses are connected to the charcoal canister. Remove the right inner fender well to allow access to the canister. Remove the canister by pulling it up and out of its mount. Disconnect the hoses and the electrical connector. Connect a length of hose to the valve, then tentatively suck on the hose - air should flow. Blow through the valve - air should not flow.
Most issues with fumes are not related to the canister, but to fuel leaks or oil getting onto hot surfaces.