I have and 88 Iroc camaro with a tpi 350 and every time I fill the car up without topping off or anything when I drive gas starts to leak out gas cap on to my quaterpanel. I have already read a post on the subject they said "believe it might be the tank pressure control valve up by the emissions canister."
someone on that thread said that that fixed their problem. I dont know where the emissions canister is located or that it looks like and I was hoping some one could show me a pic and maybe pass along some useful info on fixing my car.

 

Same on mine, I haven't replaced the gas cap but I start the car and then retighten the cap... seems to work. I have some rust coming through so I just don't fill it up that much

 

I'll have to try that, thank you for the tip