The fuel tank is in the trunk, if there is inadequate sealing where the fuel gauge sender is installed, there will be odor. Also, look at where the fuel fill tube enters the car. There should be a rubber gasket around the tube, which can be seen when the filler door is opened. If the gasket dries up, it may leave a gap where vapors from the filler neck and cap area can come into the trunk. I have a 1985 Mercedes that has a bit of a leak from the cap itself when the tank is full, and the fuel can drip down the fill neck into the trunk because the gasket there is not sealing good around the neck.

Other owners have also reported having cracked rubber fuel lines under the car around the pump and filter. It could also be a damaged fuel line or injector up in the engine compartment. For your safety, have the air filter assembly removed for better access and inspect on top of any engine surfaces for pools of gas that have leaked out and accumulated. Sometimes a technician can use a 4 or 5 gas analyzer to find a fuel vapor leak source. Usually the analyzer is stuck in the tailpipe to "sniff" the exhaust for emissions. One type of emission they check for is unburned hydrocarbons (raw gasoline). So the analyzer can be used to sniff around the fuel tank, engine, and fuel lines to locate a leak.