Definitely enjoy the challenge to root cause and resolve issues, but wanted to reach out to the Mopar Doctors for input.

A little background on the issue. I stopped by my friend's house yesterday to drop off some parts from Carlisle and noticed a slight fuel vapor smell in the garage (racing fuel). I began to walk toward his car (A-Body) and it was obvious the smell was coming from the rear. He mentioned fuel was recently dispensed (roughly 3-5 gallons) into the tank (non-California emissions) and started up outside the garage. The car was pulled back into the garage and not touched. The fuel tank is probably 1/2 to 3/4 full. There is no evidence of fuel leaking, so my initial thought is to raise Mopar up and check that the fuel vapor lines are fully seated. It's not a strong odor, but definitely present. I don't believe it's due to the warmer temps?

Anyone else experience a similar issue? Anyway to check that the fuel filler pipe grommet to the tank is fully seated once assembled? If I recall correctly the grommet has a slit that sits on the edge of the fuel tank opening?

Thank you in advance for your input!

Saying "A body" is functionally useless.

My 72 Dart, an A body, had a charcoal canister to absorb fuel vapors. My 65 Cuda, another A body, does not, it has an open vent. I would not expect the 72 to smell, I would not be surprised if the 65 did.

So depending on what A body it actually is and whether or not any emissions devices, if there are any, are hooked up no one can answer your question.

A-Body: 70 Dart

One other note is his garage door does not open much…. works a lot.

In 1970 Mopars didn't have charcoal canisters to filter the fumes from the vented air. Even the California emissions didn't have them, only a vapor separator to prevent fuel from spilling out the vent and the fumes were released into the crankcase.

Warming weather can cause more of an odor.

My suggestion is to check everything about the fuel tank for any wet spots and then fill the tank.

Give it a little bit of a run making sure the slosh the fuel a bit and look for wet spot/leaks again.

Anytime I had the fuel smell it always was a leak. When they are small they are hard to find especially in hot weather because it evaporates so fast it doesn't leave a wet spot. The last 1 I had to find was a drip out of the connection on the fuel sender.

How about the used empty fuel jugs stinking

There's always 4 or 5 cars in my 30 x 40 shop - including '68 & '69 Road Runners, and several fuel jugs, some empty & some full - no aroma unless I open a jug to gas one up.
If I light one off just outside the shop but the tailpipes are almost in the shop, I can smell some exhaust, but no gasoline.
Only time I've ever smelled fuel in there was from an open jug, or a spill, from working on one of them.

Running stock/steel or aftermarket fuel hose?

I've found rubber a/n fuel hose can smell strongly of fuel vapor. I use only teflon now.

What or where is the "fuel sender" ?

It's the float assembly in the gas tank that sends info to fuel gauge. They have terminals where the wires hookup that can leak.

"Racing fuel" depending on blend it could be eating a rubber hose or gasket.

How is the tank vented?

My car with an.open vent hose on the cell always smells like gas.

I had the same problem with my 67 Plymouth the rubber fuel fiiler hose was was sold as fuel line and it was for water changed the rubber hose to a fuel rated hose and the smell disappered. This the rubber hose that goes from the filler neck to the tank, I had an alluminum replacement tank made and did away with the rubber dougnut mine connects straight to the tank..

.

The empty VP jugs were checked and sealed.

The fuel tank setup is stock.

Reproduction steel fuel lines, then there is a small section of rubber hose between the sending unit to the steel fuel lines. I'm not sure on the sending unit if reproduction or rebuilt OE. I will need to follow-up on the sending unit, but the unit is installed in the fuel tank original setup.

The fuel tank and carburetor bowls are vented to the atmosphere.

Between the two, there is some evaporation at all times. In a fairly well sealed, not particularly well ventilated structure it will usually be noticeable.

One leak I had that was causing the garage to smell was at the mechanical fuel pump. Wasn't a big leak it would just sweat enough to get the fitting wet but not enough to even drip in pan under it.

There is an indoor fan that turns on in the garage for a period of time during the day, but his main garage door does not open that often. They have a standard pedestrian door attached to the garage that the family uses to enter/exit. I told him to open the garage for a period of time to see if the smell goes away.

The 70 Dart was filled (1/2 - 3/4 full) with fuel outside of the garage and then pulled back into the garage where it has sat for at least two weeks. I'm going to reach out later today to see if he went underneath the car over the weekend to see if there were any signs of fuel leaking.

I went to great lengths to seal/insulate mine, and so far this has been the only drawback.
After opening it up and doing an air exchange for a few minutes, it's fine for quite awhile.
If the smell comes back immediately after being aired out, there is probably a leak somewhere but as said, definitely something to watch closely.