Name that odor!

[Sklptrljay]

So I have noticed that when I leave my truck out on a warm/hot day and have left the windows up, there is a nice smell waiting for me.
At first I thought it was a chemical smell, almost like when you smell burnt plastic. I had not left it out like that again for a while and kind of forgot about it. But, yesterday I left it the same way and when I opened up the door, there was that smell again.
Now, I'm thinking that it's fuel causing the smell. Obviously if it's a fuel leak I'll get it fixed, but I was wondering if anyone else had a problem like this. And if so, was there a certain spot in the fuel system that might be more susceptible to leaking when left in the heat.