I have a 2003 Chevy Monte Carlo SS 3.8L with 181k miles, which recently has developed a fuel smell inside the cabin after it sits for a few minutes.
I left some cardboard under the rear of the car by the gas tank and under the trunk area, and came out this morning to find a small black puddle that did have a very gassy smell to it. I looked under the hood at the rail, regulator, lines, injectors, etc. just to make sure nothing was leaking, all checked out. I crawled under the car and looked at the fuel lines, one of them by the fuel filter was rusty but wasn't wet and the rest of the lines don't have any rust at all all the way to the rail. The fuel filter wasn't wet either, and I didn't see anything else wet.
Has anybody else experienced this on these W-body cars (monte carlo, impala, etc?). Are there any common areas that are prone to leaking fuel?
Just looking for a starting point.
Thanks!

You should check your canister.

BTW you likely have an evap code. Is the cel on?

Nope, no CEL.
The canister is ontop of the gas tank right? So the tank would need to be dropped to check it?

The canister is near the tank. NOT on top. You will see plastic lines from the top of the tank going to the canister and from the canister to the front of the engine. The black fuel is a dead giveaway that it'* the canister.

What is directly above that spot on the cardboard?

I couldn't tell, my plan tonight is to back the rear end up on ramps and leave the cardboard under it again and crawl under it tomorrow morning.

Although it'* obvious gas is getting on the ground, it isn't leaking all the time (and there'* only a small puddle each time). I haven't established when exactly it leaks but am working on that. But even with losing gas, my MPG doesn't seem to be any different. But there is a puddle coming from the rear end somewhere that'* dark and smells like gas. This car is starting to cost me some serious $$$