I put a gasoline container with just a bit of fuel in it in the back seat of my car for a few days last summer. I noticed the gasoline odor when I next drove the car and took the container out soon after. The odor remained. I burned a candle in the closed car for several hours, and that seemed to reduce the odor but didn’t eliminate it. I still notice the odor every time I get in the car, even six months later. I don’t think any gasoline spilled from the container, but the odor remains.
Even if you did spill some, gas evaporates pretty fast. Just having a gas can in their for a days, I’d have thought the smell would dissipate within a few hours.
If covering it up doesn’t work, maybe try something absorbent, like activated charcoal. If you have a cabin filter, I’d replace the filter with a HEPA filter, if possible, and run heat/ac on recirculate for a while and leave the windows cracked when you’re not driving it.
But 6 months later?
Can you smell it before you get into the car? My concern, at this point, is that it’s not coming from inside the car, but rather you have a fuel leak somewhere. Next time you drive somewhere, after you get done, you could try looking/smelling around under the car as well as in the engine bay and see if you can see or smell anything.
I keep the car in the garage with windows closed. I don’t smell anything in the garage or when I get near the car, but I immediately notice it when i open the door and get in.
Then it’s probably not a leak, but like I said, gas evaporates quickly.
I’d still go with some activate charcoal and/or leaving the windows open overnight.
If you have a (household) air purifier with a HEPA and/or charcoal filter, you could set that in the car and run it for a few nights.
Also, now that I think about it. Look in every nook and crannie of your car with a flashlight. Under the seats, in the trunk, glove box, under the dash, pull the blower motor to check in there if you’re handy and make sure there isn’t a dead mouse or other small animal putrefying.
A while back my garage smelled like butane. I spent half a summer trying to figure it out. I took everything in my garage (blow torches, propane tanks etc) out and it still smelled. There’s no natural gas lines running near or through it, but I looked into that idea as well. After a few months of trying to figure it out, it ended up being a dead, decaying squirrel. Oddly enough, when I was looking around on the internet trying to see what could make my garage smell like butane, ‘dead squirrel’ came up a lot but I kept dismissing it.