Do you still have the charcoal canister in the engine compartment? It would be behind the left headlight.
Can you look at the front top of the tank and tell us how many fittings you see coming out of the tank? On a 71 or 72 you will see 1 on the right front, 1 in the center, and one on the left front. There will also be a 3/8 fuel line running from the top of the tank, from the fuel pickup/sender tube, to the engine.
Do you see a series of 4 pipes coming from the axel hump area ahead of the tank just above the rearend.? They lead to an area behind the back seat.
Let's see what you have. There are a few ways to tackle this. Some will offer some relief, but the best setup is the full 71-72 vapor recovery system.
Currently, it sounds like you are not running any type of vent. You can build pressure or vacuum depending on conditions. The pressure can force fuel past the needle and seat of the carb when parked hot. The smell will be coming from the engine area and is most noticeable if you have an open element air cleaner. This will also lead to starting issues in hotter weather.
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I have just restored my 1971 Chevelle. I installed a Pro Flow fuel injection system. I did not need the vapour lines or the charcoal cannister, so I took them out. I capped all the vent holes in the tank and rear cannister with rubber vacuum caps and put on a vented gas cap. I also made sure that where the filler tube meets the gas tank is sealed because when I installed the new tank I had to make adjustments. No gas smell and all works as it should. Now if you are using a carburetor then you probably need the vapour lines so the steel lines are an easy install and do things as shown on the drawing . The line from the charcoal cannister to the carb may require revision.
71-72 Fuel tank vapor line kit.